Where can I find refills for older pens?
Since we specialize in vintage pens, we do not usually sell refill cartridges other than examples of obsolete design, most of which are no longer functional and are chiefly of interest to collectors. And though we try to keep up, the variety of proprietary refills offered over the past few decades is truly vast. We can offer the following tips, however, and suggest that if you need further assistance you try an online search, since pen hobbyists are constantly trading tips on adapting and substituting for obsolete cartridges. Note that fountain pen ink cartridges can be refilled using a small syringe, and with a bit of ingenuity a sac can be grafted onto an old cartridge to make a converter.
Parker cartridges and converters for both fountain pens and ballpoints are available everywhere and have maintained compatibility throughout all their years of production (one small exception: in some cases the fat earliest-model converters will not fit inside some extra-thin fountain pen barrels). Parker felt-tip (fiber-tip) refills have not been made in many years, but in many cases (such as the Parker 75, and USA-made 45) standard Parker rollerball refills will fit with no modification necessary. The rollerball refills will not fit the slenderer fiber-tip models, however, such as the Parker 35, but we are now selling adaptors that permit use of cut-down BIC refills in these pens. Liquid Lead refills have not been made in decades, but a cut down BIC ballpoint refill can reportedly be used in a Liquid Lead pencil (though there will be nothing to cover the nonretracting point).
Waterman cartridges and converters for older fountain pens such as the C/F are no longer widely available. In the USA, you may still be able to buy Waterman Lady converters that fit the C/F and other older-generation pens directly from Waterman (call 800 523-2486). They may also be bought from at least one active eBay seller in France. Waterman mini cartridges (also sold as Lady cartridges) will fit the C/F, and are not hard to find. Note that they may be a tight fit, and are recommended only for the earlier pens with the metal cartridge socket. When removing, twist clockwise rather than counterclockwise, so that the socket is not inadvertently unscrewed. Short international cartridges by other makers are normally thicker that the Waterman-made ones, and will not fit. NOTE: We have recently heard that Franklin Covey refill cartridges will fit C/F pens, but have not had the opportunity to verify this ourselves yet.
Small international cartridges, cut off at the neck, will reportedly fit both Esterbrook and Wearever fountain pens. There are also adaptors that allow Parker cartridges to fit Esterbrooks -- old time production, but worth seeking out. It may be simpler to use Platinum cartridges or converters, however, which reportedly fit with no modification required.
Unlike Parker's Liquid Lead pencil, Waterman's "fluid lead" ballpoint pencil used a refill the same size as the company's contemporary ballpoints. While Waterman's current-production ballpoint refills will not fit their older pens, Must de Cartier ballpoint refills will.
Replacements refills for Sheaffer and Eversharp ballpoints of the 1940s have not been made for decades, but a number of hobbyists have made and sold adaptors, as well as posting do-it-yourself instructions online. It has also been reported that Eversharp ballpoints of the 1950s such as the Star Reporter, Reporter, and Kimberly can be used with Cross refills, though some tape may be needed for a proper fit.
Esterbrook ballpoint refills for their click-action pocket pens are no longer available. If you are determined to restore an old Esterbrook ballpoint to use, you can follow the instructions here to adapt an original Esterbrook refill to carry a modern mini ballpoint refill. Ballpoint refills for Esterbrook desk pens may still be available, in the form of refills for the Berol Recorder (which would appear to be the same product, now under a different brand name), but we have not yet verified this ourselves. Recently we have been informed that Lamy M16 ballpoint refills will fit, though will protrude a bit farther than the originals when extended. The plastic cap must be pulled off the back of the Lamy refill first, however.
UPDATE: We have received conflicting information regarding the use of Lamy M16 refills in Esterbrook ballpoint pens. One correspondent reported that they will work if you pull the plastic cap off the back end of the refill, though extending slightly farther than the originals when extended. Another correspondent reports, however, that they will not work at all. Perhaps the Lamy refills will fit some Esterbrooks and not others, but we have not been able to make a proper study of this ourselves.
UPDATE: Many of the workarounds for ballpoint and fiber-tip refills appear to have been made obsolete by the spread of 3D-printed adapters. One such adapter for Esterbrook ballpoints is available from Bamapen, while a broad selection of other adapters is listed by Tofty.