Just come across this topic - not sure how much money people are paying for these launch wheels but most of the various commerical sets seen over the years are silly expensive.
Here are some posts from previous discussions, a version of the ones shown above are very easy to make yourself with off the shelf parts and no welding necessary:
Main pics are in this first link: Beach launching
Launch Wheels For Aerotec
Launching wheels DIY
What looks slightly concerning about some shown in this current topic is the narrow tyres, I tried narrow pneumatics and they were terrible compared to the wide (F1 type solid slicks) type which rolled so much easier on shingle, pebbles, even sand.