I bought mine at a full line plumbing store. It was called Oneida Plumbing supply. Any plumbing store will have them, but you might not find them at the big box stores.
Don't get too hard on yourself, you are sure not the first one to make such a mistake. Just be glad you didn't get it all up and running before you found out. Most of the materials you used can be re-used. I have to run now, but I will try to give you more ideas later today.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.