Most of the wheels that have been suggested above have the wrong offset for an Escort. The Euro wheels from a Saab, Peugeot, Citroen etc have wheels that will "fit ok" but there's issues with offset, the stud hole size, CB size, etc.
 
If you are re-drilling the hubs, re-drill to the Falcon stud pattern (114.3X5) and fit ED/EF/EL era 15" steelies. The offset is +6 so about 6mm away from the Escort offset. They will be further towards the guard by 6mm, so much better, and the wheels are plentyful.

Forget the 15" wheeks for a rally car.... The 15" tyres you can get are not a low enough profile and will make the wheel diameter way too large... I ran 14" pug405 rims (which are a good offset for an Escort) withe rally tires on the Autocross car, but ultimately the lowest profile that rally tires come in is a 60 profile which made them taller than 13" ones. Also on a rally car you want higher profile tires to absorb the 'bumps'..... Really think the tire issue is you main problem, not the rims which are relatively easy to get if you know where to look.... Most 15" rally tires are 205/65/15 that I have seen as a minimum...

Matt - I'm with nic......I was going ddown the 15" path as well but to get a similar height of a 13/14 or 610mm you need to run a low profile tyre....650mm high wheels such off a 4WD rally car are too high & wide.  After a lengthy discussion with Stucky tyres are going with 14" wheels
with 15" wheels you would not only need to arch it but tub it as well
 

Matt- you might want to weigh up the cause and effect of going to 15's. we changed from the 175/13 dunlops to the 185/13 dunlops last season. We rarely  finished a khanacross/motorkhana/autocross or rallysprint without crawling under and replacing an axle in the locked english diff. The 185's on the same 13 6jj std alloys also ate my front arches.
we're only now contemplating 14's or 15's on both cars now weve got rid of the english axles and puchased some arches. In retrospect maybe redrilling the hilux axles was a mistake and we should have looked harder at converting the front hubs to falcon stud pattern and stockpiling falcon rims.
 
Does anybody have a guestimate on the weight of a saab alloy compared to std esky alloy
 
Steve