The trouble with Rhino tribal is that there aren't really any spells that care about Rhino spells or Rhino cards, so I'm not sure if it will ever matter. Many other tribes may have the same problem. I considered tweaking one of the cards so it mattered, but it just looked fiddly; I'm sure cards that care will come along eventually.

I put this at common assuming a Rhino tribal set; if not, it would be uncommon I assume.

It's still a bit wordy and not quite right. Originally it said "spend this mana only for Rhino spells and activated abilities of Rhinos" but I decided that didn't make that much difference.

The mana-fixing is because most rhinos are G, or GW, but there's one GR and one GWU (Rhox were Bant in Shards) and a few shapeshifters, and so a bit of fixing seemed helpful. Maybe it should just have been "search for a basic land card".

The unusual "draw up to" is because I wanted something that would care about Rhinos dealing combat damage (since they have trample) but "draw that many cards" was too strong compared to the other abilities.

I think Brass Herald in a Rhino deck will still catch this one... aww, no, it won't because it specifies creature cards. Darn.

I assumed there would be some card which cared about spells sharing creature types which would be compatible with arbitrary tribal spells, but I didn't know what it was. Brass Herald was a good guess, I still hope there's something else. But it still means there's almost nothing unless you specifically write make one for that type :)

Edit: I can't see any cards that look promising. I hoped for something like "when you play a spell that shares a type" or something, but almost everything that might say that says "creature" instead of "card" or "permanent" or "spell".