The MP Select Mini V1 & V2 use the same nozzle.
The stock nozzle has an overall length of 10mm.
Threads are M6x1.0 with a 5mm length.
Nozzle opening diameter is 0.4mm
(For reference a genuine E3D nozzle has a thread length of 7.5mm)
Malyan 3d printer 0.4mm Nozzle of M200
Exact match but cost prohibitive. $19.05 USD (Nozzle: $5.50 + Shipping: $13.55)
Malyan M180 - Replacement Tip 0.35
Exact height and thread size but the nozzle opening is 0.35mm. It is a bit expensive for a single nozzle though.
3maker J-head Extruder Hotend Copper Volcano Nozzle 0.4mm for 3D Printer 1.75mm Filament
These nozzles do not have the same thread length as the stock nozzle. The threaded side is 1.17mm shorter than the original. You can get these nozzles to work by tightening the heat break/filament guide all the way to the threaded half of the nozzle. If you miss this step filament may ooze out the sides. No idea as to why the product title has “Volcano” in it. This nozzle is far too short to be an E3D Volcano nozzle.
Any nozzle with M6 threads should work. You may have to make adjustments to the bed and/or heat break/throat. You may also want to look into using a Z Spacer.