Ed Wyatt runs a 6 pack dive charter from Belleair Boat ramp. Give him a call, 727-286-7556.
There's also "dive clearwater" with the plunger.
Welcome To Dive Clearwater! (727) 443-6731. Their schedule says 7 days a week on the website.
There's also some dive shops that have "house" boats:
Mac's Sports with the "Mac Daddy" (727) 442 - 9931
Tackle Shack 800-537-6099. They have two or three boats. No idea if it's in service yet, but they recently purchased a fast mover to run 6 diver day trips to the
middle grounds.
Honestly, though. Coming from Orlando I would head east to the Atlantic rather than west to the gulf. Far better diving, and cheaper boat rides because boats don't have to go so far to get to a deep site. Look for operators at Palm Beach, Jupiter Beach area. It's only a slightly longer drive, but the diving is far superior in the ocean. I live a few miles from the marina where tanks a lot and the other local ops dock. I still make the drive to the east coast for diving.
If you want a truly great dive, head to Blue Heron Bridge. It's a shore dive so it's FREE! Make sure to call the local shop
Force E to find out about tides if you do it. Pretty sure they will tell you tide info for free. It's critical that you dive this site in slack tide. I think there's a lengthy thread about blue heron bridge in the Florida section of the forum. The only thing I didn't like about the site was that when the tide starts changing you're done with it for the day. One tank (or rather part of a tank) only.