Rod and Spring are supposed to be rare items. You may find some on the map or randomly on enemy soldiers. If you don't play with "Drop All" the chance is even lower because the soldier may have one but doesn't drop it.
If you want more of them you could add them in cheat mode (lame ) or add them to a merchant or BR inventory. This would require XML editing (corresponding XML file in "NPCInventory" or "Items.xml" for BR).

Trigger Groups are Scifi items and will only show up if you have Scifi mode enabled at the start of the game. You could remove the <SciFi> tag from the item in Items.xml however, which makes them available in normal mode as well.

Just keep in mind that BR/merchant inventories take time to update. You'll have to wait a day or so before previously unavailable stuff may appear.