I do believe there was a shop in the usa selling these for honda's. Just google for clear motorcycle coolant reservoir.
IT DOES LOOK AWESOME THO. but do keep in mind acids from the coolant -the stuff that prevents build up, corrosion and rust formation etc will affect the pvc or plexiglass.
so it might be advicable to create a mixture of demineralized water to keep it clear.
Also its an overflow so it has to stay in shape when warm.
Definitely acids can effect the acrylic, but they need to be fairly strong to have much effect. Most coolant is slightly akaline, but can change from contamination so def something to keep en eye out for. If you are doing this mod, you are probably already changing fluids pretty regularly since it's cake for wrenchers.
There is no way this thick acrylic will heat up enough to warp or anything from the normal operation. Its like 5mm thick. The coolant entering the reservoir is certainly hot, but it doesnt circulate in the cooling system once its in the overflow. If there is already some coolant in there, as there should be, it will cool any hot fluid coming from the system instantly. But even if there isnt, it still wont stay hot long enough to cause an issue. Using the metal cap version will also act as a heat sink, so I def recommend them over plastic end caps(may help the acrylic last longer). Heat isnt a real concern for this unless you mount it in a place where it will catch excessive heat(more than the radiator radiates).
I do expect the acrylic will yellow and cloud over time if enough UV light gets to it. NBD, easy and cheap to replace.