Fear of flying.
Apparently you are no Trekkie either, or you would boldly go where (you think) man has not gone before.
There are lots of blue spruce (picea pungens) bonsai. One even won the US Nationals a few years ago. IIRC, Walter Pall has at least one Norway/European spruce (picea abies) bonsai. I know of many bird's nest spruce (picea abies var. nidiformis) bonsai, not to forget Ezo spruce (picea jezoensis - Japan native) and Engleman spruce (picea engelmannii - NA equivalent) bonsai.
I am unaware of many fir bonsai and the few I am are all sub-alpine firs (abies lasiocarpa). Otherwise, the knock is that the needle size doesn't reduce much in bonsai cultivation, so you must plan accordingly. The same seems to be true of spruce and Douglas fir (which isn't really a fir and isn't a spruce as Mauro Stemberger thinks = pseudotsuga, meaning is is botanically closest to a hemlock).
Grow
a pair three or even more of what you've got, which could be Douglas firs. The technique for making big trunks is the same as for pines and etc. = let the upper trunk run until the base is as thick as you want, then sacrifice everything above a branch you select to be the continuation of the trunk. It is at least 5 years of patience, more likely a decade. Meanwhile, maybe try to make small bonsai of what you've got or some others like them - I do this with
babies I find near my doorstep. It is fun too.