Unicomp could sell you replacement caps as well. I picked up some caps from them and they're quite nice.
Don't buy replacements from Unicomp unless you need a big order because their minimum shipping is fairly expensive.
I bought from them, and I emailed them because the international shipping choices they gave me at checkout were a minimum of $20 and they arranged $8 tracked shipping for me. I would probably order an RGB set or something if I was going to order two caps. But I agree it would probably be cheaper to buy privately. 
OK, fine, that's Canada. From USA to Canada probably there are inexpensive options.
When I wanted to buy from them 2 years ago, shipping to Singapore, I remember a huge figure like $46 or something (Fedex.). This may have changed, but I have been using a bulk proxy since then so I don't need direct shipping which is almost always more expensive.