Howdy, and welcome to FWM!
Yer best bet for any of those fish would be to talk to yer local LFS and see if they can order them for ya. If not, a search on-line will result in plenty of websites from which fish can be ordered. Most of the species on yer want list are not commonly offered and will probly require ya to order from a specialized dealer.
Most of the fish on yer want list are gonna be limited to a single fish or a pair in a 75 gallon, possibly with a few smaller fish for variety. For example, in one of my 90 gallon tanks, I have a 13" redhead, a 9" blackbelt, a 6" salvini and several convicts, which were feeders that didn't get nommed on. The dovii and umbee should easily reach 18" or more as an adult and in reality are too large for a 75 when fully grown. They really should have a tank with a 6' x 2' footprint, i.e. a 180 gallon or larger.
The only way to limit growth is through poor water quality and/or poor nutrition; the concept that a fish will only grow to the size of its tank is true only if it's bein' given less than optimal conditions and it's growth is stunted. With all due respect and not lookin' to offend, but hopin' to help ya out, if yer fish are limited to 5" plus or minus, then they are not reachin' their full potential and their life span is gonna be severely shortened.
So many fish, so few tanks.
"In the fields of observation chance favors only the prepared mind." - Louis Pasteur