Yes they were,my fist three wheeler i rode was a Honda 1983 200e.Douglas rims were sold back in the 80's.They can be found on ebay.They are made of aluminum.There bolt pattern is 3/100.You can change the rear hubs from a Tri Z they are a 4/100 bolt pattern.Them there are all kind of differant rims you can use.
I thought abought some cutom work on the front rim and tire.Just havent got around to it yet.Does your Tri Moto have a K+N filter?