Recently one of the oblong glide rollers for my futon broke and I searched the internet for a replacement and found that only one or two places carried them at a cost of $20 - $25 a piece. After some quick measurements and a couple of prints later, I now have 2 printed glide rollers that ended up costing maybe a couple of bucks. If you have a futon that uses these, I highly recommend downloading the file.

You will need to find the right metal pin / dowel that is right for your futon.