what's wrong with the 4x130 spare? When my bug was 4x100 and 4x130 pattern I drove on 4x100 wheels and kept a stock 4x130 spare wheel. Just remember to keep both a 17mm and 19mm wheel brace and a set of stock bug wheel bolts.
Failing that, visit a scrap yard for a spare wheel. I had a 15" skinny space saver wheel and tyre from a Jap import Mazda for a while. Beware getting an alloy spare as they're usually pretty wide and will take up more room in your luggage area. (not such an issue in the 1303 as in the torsion bar bugs though, you're lucky in that sense)
If you've got disk brakes on the front you'll need a 15" wheel, if you've got drums all round you can get away with a 14" wheel. It might widen your options.
just out of interest, because I've got 5x112 hubs all round now (not redrilled so the 4x130 pattern is gone) I have to carry a 5x112 spare. I've got 16" steel wheels on the hubs and a 15" steel spare with a Porsche/Vredestein collapsible spare tyre. I have to carry a small 12V compressor to inflate it should I need it but it looks cool
