Hi
As far as I know any 15" Ford fitment alloy wheel should be fine
Mk5/6 Escort, Mondeo & the likes
If memory serves me right the PCD is 4 X 108 & ET of 38
Here's a little info from Alloywheels.com
Make : Ford Model : Sierra Year : 84 to 94 PCD : 4x108 Offset : 35 to 45 Bore : 63.4
Most 4 stud Ford rims seem to fall within that range
Have a browse here
Alloywheels.com