When Marcel needed it, NO ONE in town had it (???) - so I got mine overnighted from here:
Tylan 40 Premix Powder - 340 gm jar (12 oz.)
I'm going to PM you as well (I got your PM

), but probably won't get to it until tomorrow

.
You might have your friend call the manufacturer directly as far as potency - but I think they'd supply the same types of things/potencies. Maybe calvet can tell you a number from the Tylosin jar?