Both Slavex and JBD are correct. You can gear up to participate with a Ruger P-85, and once you start IPSC you will almost-certainly be deciding to move from the P-85 to something more contemporary. Either way, for IPSC, you'll need a suitable pistol, 4-5 magazines, a suitable belt, a suitable holster, and at least 3 magazine pouches. Wisely chosen, the belt (and I suggest 1.5") can be used with any subsequent pistol, and - wisely chosen - the magazine pouches (again, I suggest 1.5") can be used with a subsequent pistol. Magazines, however, will not work with anything else, and any money you spend on magazines and holsters is money you could spend on magazines and holsters for a much more appropriate pistol.
Right now, the question in my mind is this: how invested are you in the P-85?
Is the P-85 new to you (and do you have only 2 or 3 magazines for it), or have you shot it for years, and know it intimately (and you already have 4 or 5, or more magazines for it)? If it's the former, you should follow Slavex's advice and cut your losses now, before you start spending (limited) money on gear that is made just for it. If it's the latter, however, and you already know that you can operate your P-85 at a high level (or at least high enough to meet the Black Badge standards) and wish to stick with the P-85, by all means, find yourself a suitable holster for the P-85. (Good luck.)