It's hard to recommend a vendor because there are tradeoffs with each one.  For an Amazon-like experience, 
Nexaph is good and ships from the US, but the cost is higher (sometimes much higher though they do monthly? prebuys).  For trying single vials, I would suggest 
Deb.  She is in the US as well as resells vials from Nexaph and Uther.
SRY is a popular 
vendor based in China, and I haven't had a problem ordering for delivery from their US "warehouse."  I haven't ordered anything shipped directly from China yet since I am still paranoid about seizure, even though vendors normally reship.
Related thread: 
triz-whats-the-average-mg-shipping