You can find replacement wheelsets are stores like Sears. They are usually low quality sets but are normally fine for indy film tools.
Hmm, here's a quick search on Sears:
Kryptonics Aggressive Wheel Set 55mm $29.99
This Kryptonics 55-mm aggressive inline skating wheel set includes 8 long-lasting wheels and bearings designed for street and ramp aggressive skaters.
Semi-soft rollerblade wheels are much quieter than what has traditionally been used for years in the past - skateboard wheels.
Rollerblade wheels do have one problem. They tend to squeak a tiny bit when used on curved track. Nothing that a little oil or powder wont fix but thought you should know.
The hardness of rollerblade wheels is represented by a number followed by a "A" (Ex. 89A). Anything over about 90A is fairly hard but not as hard as a skateboard wheel. I havent tested alot of wheels so I couldnt tell you the ideal hardness but I have used 90A wheels and was pretty happy.
just to clarify, both skate board and roller blade wheel manufacturers use the same "A" rating on the wheel hardness. it's just that most skateboard wheels tend to be about 96A - however you can get "old school" wheels that clock in at around 76A. that way you won't have to worry about your track sitting perfectly on the tapered roller blade wheel since skate board wheels are cylindrical. although expect to pay top dollar for those skate wheels.
Make sure to get "aggressive" rollerblade wheels because they tend to have a very flat profile just like skateboard wheels. Senate makes great quality wheels that often include good bearings AND affordable pricing too. Remember the more wheels the smoother it will glide over the joints in the track but make sure you make your dolly work on curved track as well. The geometry changes as you go from straight track into curved track so you cant just slap some wheels on a board and hope that it will work perfectly. Take measurement carefully before you build. Good luck.