You can do this temporarily using a small piece of business card or paper. You may find only needing to do it on the E string (in the B string position).
I did it sloppy but I like it like that. If the paper shifts while tuning I can pull it back into place or hold it still... (I do this on this instrument to fix a fret buzz when open as the nut has worn too low)
And to find strings, you just need to buy 4 string sets and a single High C and F to match. Most companies do not make wound F strings (.020W or .022W) so you may find yourself using a plain steel F. and Plain Steel is Plain Steel so you can use a Plain Steel string from who ever has available.