here, "is a knotty conundrum" with no perfect answer. And, an earlier post here.
Short answer: In the USA, get a rubber cane tip at a Home Depot or Lowes for the missing rubber foot.
Alternatively, try the ancient, tried and true, rite of Cannibalism!! put up a "watch" on eBay of an exact match of the Tiltall that you own - as each company changed the design of their foot "solution" [as the image above]. So, be it the original Marchioni, or Leitz, who purchased the design from the Marchioni brothers. Or, Fred Albu's Unifot and StarD, or one of the three or maybe five other iterations - get a matching used Tiltall to the one you now own. Your tasty victim can be less than cosmetically perfect. Then blend the Tiltall you have with any interesting parts, including a foot or two, from the one purchased on eBay. [And sell off the remaining Tiltall morsels on eBay - sell a handle, here, a column or leg, there, that eyeball, afar.]
More history and a selfie with the current owner of the TILTALL trademark, Oliver Yang. FYI- even the new feet of Oliver's current production of models "TE-01S, TE-01B, TE-01G" do not fit his own earlier KingHome Tiltalls. As with most everything else in life, the "show" and the "improvements". . .must go on.
The short story below - Left: Oliver's new feet. Do they look familiar? NOT. On right: Easiest solution. In the USA- Lowes, Home Depot, Ace, and most medical supply stores.