Dammit. I thought "Once available" meant "it was available for a while in the past but isn't now", not "whenever we get one", since King's Rock was a thing in E9-ish, so Politoed WAS available. *sigh* I'm stupid.
Anyways, gonna put something together here, gimme a sec.
EDIT: So here we go. First of all, let's see what can be done to improve your current set-up.
For Ninetales, I think you'd be much better just sticking with attacks than going for a WoW-Hex combo. If you go back to pre-E13, you can get it Energy Ball. There's also Extrasensory from any episode (and the in-rainbow-20% flinch chance is nice enough). Both have a 10% chance to do stuff, so yeah. With Psychic, Grass and Fire, HP Rock or Ground round out your coverage very well.
For Politoed, pre-E13 nets you both Psychic and Ice Beam, as well as (but you can skip it) Scald. Since your team is sorta slow, you could also hit up the 7th Street tutors to get Icy Wind instead of Ice Beam.
With Volcarona, HP Grass would be much better than Electric IMO, since it hits both Water and Rock super-effectively. Sure, Electric hits Flying types Super-effectively, but Rock is a much bigger threat to Volcarona.
Though I'm really not expecting this thing within the next 3 episodes at least, sadly.
Here's an odd one. Honestly, beside Cloud Nine, I don't really see much of a reason to run Altaria? If you wanna stick with it...um...give it Iron Tail for 60% chance of Defense drops? Altaria gets next to nothing good. Maybe Ice Beam from pre-E13.
I think you should run Swift Swim over Rain Dish since your team IS rather slow, so having at least one speedy thing (without set-up) is nice. Again, Scald from pre-E13. Your team also isn't that bulky, so Leech Seed stalling wouldn't be terribly effective. Try maybe Brick Break, or Zen Headbutt (Swift Swim+40% flinch chance? sounds good to me).
...eh. Medicham really isn't that good without it's mega. Yeah, hits hard, but it's slow and rather frail. You have no Electric coverage, so I'd run Thunder Punch. For a Fighting STAB, you could also run Force Palm for 60% chances to para. And I'd really recommend Bullet Punch to help with that pitiful speed. Also, maybe Rock Tomb>Rock Slide since Medicham won't be flinching anything anyways and the Speed drops can really help your team out.
Your team isn't really dependent on having weather except for setting the field effect, so I really don't think you need Rain Dance on Blastoise. Again, Ice Beam and Scald from pre-E13 are a thing. There's also Dark Pulse, but I'd instead recommend Flash Cannon.
For other stuff you can use, I'd have 5 recommendations: Sigilyph, Lickilicky, Roserade, Whimsicott and Heliolisk. Sigilyph's flagship set based around Cosmic Power and Stored Power works really well with the fact that the Rainbow field doubles Cosmic Power's boosts are doubled. That means not only doubled defenses in one turn, but also a 100 BP Stored Power in one go. Next, Air Slash and Charge Beam/Ancient Power are excellent moves to go with SP. Air Slash gives you a 60% chance to flinch the foe, Charge Beam is guaranteed to boost your special attack, and Ancient Power is coverage (but CB>AP by a mile IMO). Tailwind is also an option to support the team.
Since status moves are incredibly uncommon in Reborn, you can run Tinted Lens for "coverage" instead of the common Magic Guard, though there is a Life Orb in the game (not 100% legally, but hey).
Lickilicky not only gets Cloud Nine, it gets stupidly good coverage. It's insane how many different moves this thing can run, the majority of which have some added effects (E12 is this thing's best friend). Of course, Normal moves are amplified in that field as well and Body Slam also has a natural 30% chance to para stuff. You can also have it go the defensive route with those boosted Wishes, though there's no need for defensive things in-game.
Roserade gets it's Hidden Power boosted not only by the field, but also by Technician, giving you a 135 BP Hidden Power. And it also gets Weather Ball, so yeah.
Whimsicott has that priority with Rain Dance/Sunny Day, boosted Moonblast, Memento to help Volcarona's or Lickilicky's set-up and Solar Beam STAB.
Aaaaaand Heliolisk is pretty obvious considering the fact that you have a Ninetales around (Solar Power). Thunderbolt, HP Ice, Grass Knot and Charge Beam/Dark Pulse are all good moves for it.