I purchased a leather strap too as I am fond of plain brown day sporrans for non-formal wear, although I wear chain straps with my fur sporrans because it matches the metal cantle.

I would recommend leather straps to GOS particularly if you have the problem I often have squeezing past people in busy places. With the strap, you can very easily slide the sporran round to your hip and avoid the sometimes embarassing "is that your sporran or are you just pleased to see me?" moment. This is not so easy with chain straps, particularly wearing them through belt loops as the buckle will often catch.

I got mine from scotweb and there are a couple of ebayers offering them too. There are a few cobblers near me which also make leather bags etc, I checked with them and they said if I had a strap which was too short, it would be easy enough to make an extension in (nearly) matching leather which sounds like a solution that any GOS struggling to find their size could look into.