Part of the problem is that fancy guppies are extremely inbred, and some fish farms are shipping stock infected with the fish TB. Original guppies are hardy, but they are so inbred and produced in such vast numbers that problems like this are becoming far too common.
Pure strain Endlers may be a better bet, being much less inbred and not produced in anything like the numbers, yet, that guppies are. Smaller fish too.
But be sure they are not guppy hybrids, which may not do as well as pure ones. Female Endlers are silver, plain, only males have color. Can be lovely, but you get about 8 or 9 females to each male when they have babies. Just FYI.