What kind of lead and erasers do older pencils take?
The standard lead diameter from around 1915 up until the 1930s was .046 inch. The exact metric equivalent would be 1.168 mm, so this older standard lead may be seen labelled as either 1.1 and 1.2 mm, or even 1.18 mm. There seems to be no problem with interchangeability, no matter which metric designation is used.
Old .046 inch lead is still widely available at pen shows. In the USA, Scripto still sells a 1.1 mm lead pencil, along with refills, and Sanford sells the "Sphere", another pencil that takes 1.1 mm lead; both are widely distributed. Another brand of that still uses 1.2 mm lead is Yard-O-Led; refills should be available from larger pen stores. Autopoint is yet another manufacturer that still makes thicker lead and the pencils that use it; Autopoint labels their lead as 1.1 mm.
"Slim" lead of 0.9 mm (.036 inch), used in most pencils from the 1930s through the 1960s, is still widely available, despite the continuing onslaught of ever-slenderer leads in the last couple of decades.
We now offer a selection of both 1.1 and 0.9 mm lead in various grades and colors on our Nibs, Parts and Supplies page, as well as 1.5 mm ("VS", commonly used in Victorian-era propelling pencils by Mordan et al) and 2.5 mm.
Larger leads, used in special marking pencils, may be a bit more difficult to find. The most commonly-used thicknesses were 2.0 mm (.075 inch) and 3 mm (.120 inch); broker's pencils typically use 5.5 mm (for which one can use Montblanc "Sketch Pen" refills). 2.0 mm lead is still a standard size and easily found at any art supply store, especially one that carries drafting supplies. For other thicknesses, (>Jerry's Artarama carries both 3 mm and 5.6 mm lead).
Some Victorian pencils use "M" lead, which is slightly thicker than 1.0 mm (typically running 1.03 to 1.05 mm) and quite hard to find. In some cases, dealers will drill out the nozzles of such pencils to 1.1 mm, but such an alteration is irreversible and significantly weakens the nozzle. Since most such pencils will not see much use, we prefer to take a length of standard 1.1 mm lead and either shave it (laying it flat on a table and scraping it with a razor blade or hobby knife) or sand it down to size (an emery board for nail care can be used). This can be done in a surprisingly short amount of time, and is a useful technique when confronted with 19th-century pencils that take truly odd sizes, many of which have been obsolete for well over a century. One other Victorian size is "H" (0.8 mm, though on worn nozzles, modern 0.9 lead will often fit).
If you are still having no luck, check with Jim and Jane Marshall of the Pen & Pencil Gallery in England, who can supply quite a few odd sizes upon request. Pendemonium is another good source for older and hard-to-find sizes of lead.
Replacement erasers are less standardized than lead, but one can usually find something that will fit -- even if that entails cutting down the long cylindrical refills sold at art supply stores. Note that many vintage pencils (among others, Parker Vacumatic, Parker 51, and Esterbrook) use a 6mm eraser; Sheaffer and others make refills of the correct diameter. Duofold pencils use a larger, 9mm eraser. Again, Pendemonium is a useful resource here.