Just make sure that you have a nice wide gusset. Like 2 1/2 - 3 inches. That way you can get your hand in there. The commercialy made sporrans are usualy completly useless. You can probably sew one from lighter upholstery weight leather easy enough. I use upholstery weight leather, with 1000 deneir ballsitic for extra structure, and inside pockets.
You can also make a Kilt belt with upholstery weight leather. Most Kilt belts nowdays have velcro for the adjustment.
For a shirt you might look into a highland / "pirate" style shirt. Often they are made from tacky looking muslin, and overpriced. Personaly if I make one it would be with a nice linen, or better yet a Hemp/linen blend as it has a much better old timey look.
For off the peg shirts that work well, in the $40 range.. try a cowboy wear store. The old timey formal wear, (wah Maker brand) has some nice shirts. They have shirts that work for casual all the way to formal. (like the Hellfire dragon Tuxedo shirt, best $80 I ever spent....)