I did some more research into Finnish navy. Data from here (translated from Russian).
At first, Finns got 6 gunboats, 10 destroyers and 18 minesweepers (incl. 2 240-ton ones, which would be large by that time’s standards). Those ships were leftovers after the Red Baltic fleet departed for Petrograd (pre-WW1 Finland had one of the Russian Empire naval bases, as well as a naval yard), most were either badly damaged or not completed (and so could not be taken to Russia).
Then in 1920, by the Treaty of Derpt, 7 destroyers were transferred back to Russia. I presume those were the better-preserved ones.
During 1920s, no noticeable military shipbuilding took place.
In 1927, first shipbuilding program was accepted, which required the construction of:
- 2 coastal defence ships;
- 3 500-ton submarines;
- 1 100-ton submarine;
- 4 15-ton torpedo boats;
- 1 sail training ship.
Up to 1939 no further construction was planned, despite foreign advisors telling the government that they needed much more naval units. Situation was so bad that at the start of WW2 both Finnish monitors (powerful and modern on their own) had no proper escort ships. As a result, Finns relied heavily upon Kriegsmarine support in their naval operations.
Units active during WW2 (incl. newly built, captured or remade from civilian craft):
Ice breakers (yes, those were armed!)
Take note that there are NO destroyers of any kind listed. Oops. Tough luck facing any of the great powers on the High Seas.
Separetely from the above, Ladoga Lake Finnish flotilla (as of 1943-1944):
2 x Siebel Fahre (ex-German) - 2x102mm, 2x20mm guns (never seen a pic of that vessel in this config)
4 x AFP (ex-German) (maybe MFP, but armament listed includes 2x88mm, 1x37mm and 1x20mm which corresponds to AFP quite well)
4 x VMV patrol boat (ex-German), 57mm and 20mm gun on each
3 x torpedo boats converted to minelayers (torpedoes removed, 1x20mm gun and 3 mines fitted)
Onega lake flotilla:
3 x armed steamers (2-3 75mm guns on each, plus some AA guns)
1 captured BKA-1125
10 motor boats, details unclear
Some more info is in the Wikipedia.
In general, there seems to be no easy way to find good drawings for most of those. So, we can use German and Soviet units as much as possible, and maybe we should ask some Finns in the lobby for more info - they may have better ideas as to where to find it.