Those "triangular" towers are called Rohn towers. Rohn is actually a brand name, but has become a standard word to define a product, much as Jello and Kleenex have.
I had one put up a few years ago, for the same reason. I bartered a bit, and had a guy install a used 30' with a stinger on top. This is his profession, so he comes across smaller towers, as he installs larger ones.
I can provide his contact info, just drop me a PM
One of the fab shops in Ponca made a living building the triangular towers.
Mertz inc.
don’t do them anymore but there are tons of them around that folks would like to see leave. I paid $5 for mine that I use to get reception in the shop.