Welcome. I'm in Fresno. There's a club that meets at the Fresno Rifle and Pistol Club up Auberry Rd. You can reach out to Jim Minyard, the club president. His email is on their website:
Smoking Thunder Muzzle Loaders
I don't shoot with them and I'm not a member. But they have a decent practice range & I believe that they have shoots ("competitions") once a month. It's a very small club. I don't know how much longer they'll be around. I don't think their range is open for members to use except for those once/month days. There are some very nice and helpful people there and one... Well... Not so much. For my part, he kinda ruined it for me. Can't say I have the time to fuss around with social clubs anyway.
Among the folks that I met and appreciate is Shanon Kirby, who has powder and supplies. He lives up in Prather so I like to swing by his house on the way up the hill to get stuff when I need it. PM me if you want his contact info. To my knowledge, he's the only supply of powder within a 50-mile radius of Fresno.