wow uh...you could try a gatherer search through red cards with keyword "deals" and look for commons in recent sets,
like this but i'm not sure all of those are burn spells or creatures with burn abilities. most are, so it couldn't hurt.
in just recent sets, frostling from betrayers of kamigawa, frostweilder from champions and vulshok sorcerer from fifth dawn are good creatures, and spikeshot goblin may or may not be worth a look. if you find yourself pressed for cards four ember fist zuberas (champions) wouldn't be out of place, though how effective they'd end up is questionable.
and for spells you can go for first volley as a little pinging spell, or maybe ire of kaminari, if you feel a little crazy (both from betrayers). glacial ray and lava spike from champions go well together, and both help the ire out, and if you do go with the ire, all those arcane spells wouldn't be wasted on a soul of magma, also from champions. yamabushi's flame is a decent spell, and yamabushi's storm might be alright in a all or largely common card pool.
stepping out of just the current block, barbed lightning from darksteel is out there, and good with just a common cardpool.
of course 8th edition has anaba shaman, lava axe and tremmor which aren't really great, but get the job done, and shock, which is premo, shock troops which is a little pricey, and sizzle and volcanic hammer which i don't feel educated enough to make a call on.
not to mention artifacts, which mirrodin block had a bunch of. pyrite spellbomb couldn't hurt your deck, veridian longbow might make an appearance but i 'unno. and heliophile's in fifthdawn, but if you go monored, then it's crap.
it turns out there's a lot more uncommon and rare burn than one might believe.
200
100
100
