Clen isn't actually a 17aa steroid, so its not liver toxic like Dianabol or Winstrol.
A full profile on the drug can be found here:
Clenbuterol
The write up for T3 (Cytomel)
T3-Cytomel
Assuming you live in the states, your best bet is to purchase it from a research chemical site.
With that being said, given your background as a strength athlete, a solid diet and muscle memory will wonders on its own.
I've heard some horror stories about Clen, and it's something I would personally never touch.