The answer is always the same:
Use multiple addons in combination or build your own one
(you might get the idea about different addons VS. 1 addon for all if you start to code, maintain after each patch and keep it running... It's time consuming, very time consuming. Just use one of the hundreds of addons combined with others and you got less problems, believe me. Easier to be replaced, easier to be fixed.)
There is another addon which stocks up items at the vendor. I think the name was even stockup.