Where can these tile carriers be bought?
Most should be available from the webshop (some sizes just went out of stock I guess...) :
If you're in Europe, 3U-shop has all the sizes possibly available with M3 rails. It may be a good occasion to also get some NLC kits :
Schneidersladen only has 10/14/20/24HP with M3 rails.
In the UK, Elevator Sound has 6/10/12/14HP with M3 rails, while Signal Sounds have 10/14HP only in both M2.5 and M3... And Thonk should soon have all sizes with both M2.5 and M3 rails!
In the USA, Mission Synths has 6/10/12/14HP and Perfect Circuit has the full line, both with M3 rails only.
All of the links are indeed on the "dealers" page :
A 28HP version may be available by the end of the year, and prices for the full line should be slightly adjusted by 2022.
As of now, these only work with modules in Intellijel format. Prototypes have been assembled already for a hybrid Pulp Logic / Intellijel version, and there are cases in which it's rather difficult to use, so these haven't been released yet.