Maccarri doesn't have a 'drop-in' replacement. Rich in Mich offers a kit with custom guides and a different spring, but it does cost a few bucks. You could always send the rifle to CDT for a complete workover - he has lots of happy customers but, again, it's gonna cost more than just the parts.
The closest thing to a drop-in is a Crosman Quest spring and tophat, which goes for about $12 shipped as I recall. The Quest spring does fit on the existing guide a little more tightly than the Gamo spring and seems to reduce twang at the same time. Power is about the same.
Opinion is split on the quality of this spring, though. CDT doesn't really like them, he says they don't live that long. Rich says they last just fine, longer than Gamo's original springs. Personally, I've never busted a Crosman spring either in my Crosman guns or in several of my Gamo's that have them. Perhaps I just don't have enough shots on 'em. Oddly enough, though, I've had 3 BAM-made guns from a few years ago, and ALL of them busted their springs. BAM makes the Quest, so my good luck with Quest springs reflects either luck or improved QC on BAM's part. I have no idea which it is.