The re-railers are made by Bachman, Atlas, LifeLike, Model Power and other companies that make and sell inexpensive train sets and thyey come in the set. I guess you could call them Toy Tain sets. They have their own section of track, Brass track I believe and besides re-railing a car they are also designed to look like a highway crossing. They have been available for 40 yrs at least in HO/OO Scale in NA and in other scales too.
At times on eBay.ca there will be a bunch of brass track for sale and there's usually 2 or 3 re-railers included. I just did a quick check on eBay.ca now at this address " http://cgi.ebay.ca/HO-SCALE-TRAINS-ATLA ... 4ce3924579
" there is a 2 pack, new, for $6.75 US and it's a "Buy it Now" item and there are 8 available.
I should add that I just typed in 'rerailer' when I did the search on eBay.ca and came up with 36 hits. Not all HO scale though.
Hope this helps.