[ecz]

how an high skilled fencer could survive against a competent crossbowman?

he should not, apart the help of allies and terrain and luck. That is very realistic.

I think that a GM should make some weapons hard to find/buy/use.

Several in-game restrictions to prolong the fencer's life (not involving any house rule) could simply prohibit the use of missile weapons to not authorized people, or raise the cost of an heavy crossbow -from the wrong because too low $ 80- to the double or triple ( an heavy crossbow was an elite-weapon used by nobles or specialist troops not left to everyone working two weeks as police recruit ).

But this last point risks to move the discussion off topic : the too low cost given in the table for heavy weapons and armor if compared to the high pay of certain jobs that makes virtually anybody able to buy anything in the short period.