Here a common brand is "Lexol".
My wife, who builds and repairs saddles for a living, HATES Lexol with a passion. When people bring in their old saddles for repairs, the first thing she has to do is take the saddle apart and give it a real cleaning. According to her, she can tell when the owner uses Lexol to clean their saddles because it builds up a waxy crud in all the crevices which makes it absolutely impossible to truly clean or repair the finish. She has gotten to the point where she refuses to work on a saddle that's had Lexol used on it.

A sporran is a different animal, though, so YMMV. But personally, I stay away from Lexol because of that. For regular cleaning of leather, it's hard to beat good old fashioned saddle soap (you can use Murphy's Oil Soap too, which should be available in any store that sells household cleaning supplies).

For a really old sporran where the leather finish is cracked and flaking off, there probably isn't going to be much that can be done for it. Although I will say that there's a great product out there that I have used on old saddles, boots, and other leather products that get a lot of scratches and need a rejuvenation of the finish. It's called Blackrock Leather 'N Rich. The stuff works wonders in restoring color, blending in scratches, and giving old leather a new shine without applying an actual new finish to it. You just goop it on the leather, rub it in, and buff it.