Do you have a serial number or something else that uniquely identifies it as *your* raft? In that case it might be useful to report the theft to the producer and possibly some outfits in your local area that service liferafts. Perhaps in the future somebody will come along to register it, or have it serviced. At the very least that gets flagged then. Hopefully.
Also, if the liferaft contained an EPIRB, ELT, whatever, might be useful to inform the SAR authorities that it was stolen so they don't come knocking on your door as soon as they receive a signal from that one. Preferably you want them to come knocking only once they've found the thieves (in distress - serves them right!).
Keeping an eye out on eBay and other auction sites, and perhaps the notice boards on flying clubs in the area, does seem like a good idea too. Aviation liferafts are not the typical items that thieves keep for themselves, unless it indeed happens to be stolen by a fellow pilot. Also, the thief may not know that an aviation liferaft is different from a marine liferaft, and might try to offer it for sale at marine clubs.
Lastly, check *all* your insurance policies, including your home insurance. Home insurance, at least where I live, covers certain items outside your house too. At least that what we found out when my parents' car got stolen: the car insurance covered the car itself, but the home insurance covered the few items that happened to be in the car at that time, and that could normally be expected to be kept in the car instead of in the house. Nothing major, things like a fire extinguisher, jump start cables, towrope and such. Perhaps a life raft would be covered under this category too. (On the other hand, if there's no clear sign of breaking and entering, ie. damage to the plane, you have a weak case.)