How to find SMD transistors library for Altium Designer?
Probably the easiest (and fastest) way is actually building up your own library. You could use the vault too, but don't ask me how that works ;).

Go to File &gt; New &gt; Library &gt; Schematic Library to build a symbol library. If you open your [library].SchLib theres a handy wizard (Tools &gt; Symbol Wizard).

Go to File &gt; New &gt; Library &gt; PCB Library to build a footprint library. The two IPC Wizards you'll find in your [library].PcbLib under Tools &gt; IPC Compliant Footptrint ... are, at least in my daily worklife on of the killer features of Altium.