In one of your posts you said you owned about half of the working Larks. About how many of them are out there?
Well, now that you have called my bluff on that statement, I will admit I was exaggerating. I have 3, but only one is complete and functional. The second is missing the extractor, and will function when I use the extractor from #1. The third is missing several parts. Parts for these guns are a problem. Bob's http://www.gun-parts.com/index.html/
has a few parts, but not the ones most in demand. If yours is complete and functional, you'd better not shoot it too much, because sooner or later something will break, and when it does you are SOL.
It is hard to put a value on them. You need to find a buyer who recognizes the Beretta name, but doesn't know about the parts problem. Either that, of somebody who remembers the one his Daddy let him use when he was 10, and wants one just like it. Somebody like that will pay whatever it takes. Otherwise, I would guess $200-400.
The Lark never made much of a reputation for itself. It was the first gas-operated shotgun Beretta ever made. The current head of the Beretta family and company, Ugo Gussali Beretta, has been quoted as saying there were some problems with the Model 61, and that's why it was replaced by the A300, a completely different design.