First of all, wanting to have 6 SSR - of a single element no less - without spending money so far is... quite outlandish. If you have thousands of dollars to spare, you'll get there eventually. But so far, you've gotten beyond incredibly lucky if you have four SSR of the same element and haven't spent a dime.

Secondly, uh, doesn't SSR guarantee tickets have an expiry date? Check your Inventory -> Items -> Tickets. Make sure to use them before they expire...
And the current one isn't even a ticket, you draw immediately I think?

So you can't really save either.

Sanathlig's toolbox has Encyplopedia which will probably help you with quickly checking out upcoming Fire SSRs.
Having a quick look, doesn't look like Fire will be getting anything spectacular for a while. The Fire SSR Beelzebub (late April 2018) is insanely good, assuming that you like suiciding 50% of your HP in 5 Turns in a single Berserk and have a guaranteed Burst ready for Turn 6. And then you can do it again. On some content, that's just not feasible as you'll wipe during those five turns, but my god, nothing is going to stop a Beelzebub Fire team from getting MVP in raid content thanks to that free pot you get.

I'm not sure if you can upgrade your absolutely insane team with the first miracle ticket. Your options would be Enma (who basically cannot use since Amaterasu has a better B debuff) or Acala, and I don't think either one would make it into your top4. The second miracle ticket would also offer you Uriel or Daji, neither of who looks spectacular. Once there's going to be a third miracle ticket, I guess Mars, Beelzebub and Ra will be options. But again, against your current team? I don't think they can fit in, aside from Beelz in some content.

Maybe you should just start building a Thunder team to counter Water events instead?