Diaphragm sizing help

Larissa
Does anyone know where I might be able to buy an inexpensive set of fitting rings for diaphragm fitting? Teo different offices near me, their sets do not go higher than 85mm and my doctor told me she would like to try and see if a 90 fits. I don't want to spend another 70 bucks or more on a diaphragm. I already have wasted money on a 75 and 80mm.