This isn't quite what you're asking for (still sorted alphabetically), but you can enter "#>100" (no quotes, use whatever number you want) to show only the items you have a lot of.
You can't quite do this, but if you type "#>20" (no quotes) into the filter field it will only show things that you have more than 20 of (still alpha-sorted).
Just one question: Where, in your opinion, would be the most obvious place to look on the wiki, provided that we made this information available?
Edit: Okay, after some digging through the Mafia source code (relevant bit here), it turns out that those two are the only filters (in addition to the obvious, substring matching).
Double edit: Since the code uses regular expressions, you can even do funky things like "$<50 berry #>4" or whatever strikes your fancy.