I need to purchase a rim to have as a spare. Are all demountable rims the same? My car is a 1913 so obviously the rims are not original. Also can anyone tell me the best place to buy them?
No, they are not the same. Please post a picture of the rims you have and we will tell you what brand it is so that you know what to ask for.
Also - post a photo of your wheel/s - there are several varieties of those as well if you want them matched to the rims !
A close look at the lugs should help ID what you have, especially if HAYES is stamped on them.
As for the best place to buy, for me that would be at an auction or swap meet, as I'm very reluctant to buy new at full retail. If you want new, look here: http://www.americanvintagerims.com/
There are 3 distinct & different lug style "Hayes" rims.
If you decide to buy used, be very careful buying rims with tires still mounted on them - hard to inspect the edges for sharpness and excessive rust.