Where can I find big siding mounting blocks.

What I’m looking for is a mounting block to go on siding, but I need it to be in the neighboorhood of 7"x10". The problem is, that all the ones that are anywhere near that large are for new constuction (part of it goes under the siding, then a top part snaps over it), and all the ones for old work are too small. I’m looking, specifically, for the kind that are designed to fit right over the siding like this. Anyone know where I can get one like that, but bigger?