One in a low-level locked garage west of The Hive. Can be bought from Gang leader near helipad in Highland Park. The last Reload Speed Upgrade can be found in Montreal in Office on the 1st Floor (Restricted Area) If you have the PAX-22 combine all Upgrades. There you get a Reload Speed Upgrade and the PAX-22. Collect the Reload-Speed Upgrade and the Target-Leading System in near the Hive then head to Tai Yong Medical.
The best Way to obtain this achievement for the PAX-22 is, when your the first time in Hensha (see Video!).
