Re: Looking for parts for a 1990 Force 50
mercruiserparts dot com/selectSerailRange.asp?doc_nbr=50+H%2EP%2E+%281990%29
Or Mercurypartsexpress (dot) com
Shear pins from Mercury, part FK247, package of 6, $5
Not sure which part you mean by "tilt lock shaft".
Part #25 in the picture below, is no longer available.
But you should be able to get the rest from a Mercury dealer.
I hope this helps.