I believe they are all metric Hex keys. I found them at a local ace hardware. Also they asked me if the tiny one was for my guitar so I’m assuming they are standard for that as well. Maybe check out a guitar center or something similar.
Thats, 1,5 mm hex. But you can remove the Hotend Isolator (the part with the holes) and then screw the bolt out of the hole. For reassembly screw the bolt in your heater block (it hold the temp sensor and heater). Then screw the hotend isolator (see above) on the heater block. The aluminium plate on the photo has no thread for the bolt, so you stick the heater block with the bolt through this tiny hole.
For Ultimaker1 they included a 2mm hex screwdriver for the many hexagon socket screws. Mine was a Wera model #118068 (05118068003). Most cheap sets of METRIC hex key sets should include a 2mm wrench that would work. Ensure you get the metric set and not the SAE set.
They also provided a 1.5mm hex L-shaped key for the set screws of the z-axis lead screw. Hope it helps!