Took my car out of storage to get it ready and I noticed a chunk was gone from the space saver tire. This tire had never been used. Called a couple of tire dealers and they do not have a 115/85 R18, Any suggestions, besides getting a full size spare?

 

I bet a local salvage yard or used tire seller in your area has one that isn't too old. Maybe peruse craigslist for the latter. There are a few on eBay in that size (all mounted, except for one in Bahrain), and looks like X308, S-Type, XE, and Volvo S60 at least were so equipped. An X308 spare wheel would even likely be a direct fit without having to remount the tire, but probably would be older than those others cars' spares.