The cowl listed by Carbon Copy in the UK is actually for another Seagull model, the Razzle 3-D. It is FAR too small for the Spacewalker 120. It is not shaped right, and is too square for the firewall. Perhaps it would fit the 40 size Seagull SW model, but even this would not look right. The best solution is probably the Sig 1/4 cowl or the Fiberglass Specialties version. They make quality stuff.
Having said that, I bought a Carbon Copy cowl for the Precedent Turbulent kit I have. I thought it was fairly priced, shipped quick and painlessly, and is superb quality. It has a shiny gel coat finish. You can opt for other colors for an upcharge if you wish on all their cowls. I highly recommend them.
I too recently noticed that Horizon has very few SW 120 parts still available. When the plane was discontinued recently, any remaining spares departed quickly.
I have been flying mine for a couple of years now, and love it. I am using a Mintor 22 for power - very good match.