Maybe use some actual historical miniatures. There are probably many out there. Maybe those could work:
http://wargamesfactory.com/webstore/horse-and-musket
Also depending on paintstyle and with minor modifications those might also work:
http://victoriaminiatures.highwire.com/product/4-laser-rifles
Do you want to have an actual historical looking army as in every weapon could be created in that time or are some techy-steampunky elements okay for you?
You could build/use a flintlock rifle with a massive barrel - more like a portable handcannon - as plasma rifle.
If you don't want to be burely historical maybe some form of tesla cannon.
And what about a rifle with an array of mirrors focusing the sun into a heat ray (melta) or maybe a steam cannon fireing bursts of steam of the enemy?
And for heavy weapons teams maybe a multi barreled cannon and some (multibarreled) missle launcher. Just browse through the fantasy stuff. There are some interesting looking heavy weapons(imperium and dwarfs for example)
And i don't know how good your german are but the bitz-shop i sometimes use seems to have a bunch of flintlock rifle bitz in stock. Most of them around 10 but some variations have 40 or even 60 in stock.
http://www.tabletopbitz.de/index.php/cat/c3056_Sch--tzen-BITZ.html/page/2
They also seem to send to sweden as far as i can see. Might be a bit tricky if you don't understand the language but if you can't get them somewhere else it might be a last option.