How about ‘Footprints on the Moon’ - Howard and Raj’s filk band from The Big Bang Theory.
I definitely agree with Buckaroo Banzai and the Hong Kong Cavaliers.
Detroit Metal City(wiki)from the anime of the same name. Also known as DMC.
The Hex Girls(wiki) from Scooby Doo.
Love Händel(wiki) from Phineas and Ferb.
The Love Below(YouTube) from OutKast’s video for “Hey Ya.” Bonus points if it includes all the band members names and their back up singers, The Love Haters.
First one I thought of. (A real band from Buffy I’d like is k’s choice, who sang “Virgin State of Mind” in the episode Dopplegangland).
Yep, I’d rather have The Clash at Demonhead’s shirt. I’d also want a Munchausen by Proxy shirt (from Yes Man).
Bad News already have several.
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My name is Vim Fuego! I let my guitar speak for me!
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That’s because you’re incoherent most of the time.
Ziggy Stardust and the Spiders from Mars. I know you can get Ziggy Stardust shirts but they’re really David Bowie shirts.
Dead Leopards
I know there’s been discussions on the origins, but I heard them on 98Rock in Baltimore. Classic songs like “I want a death by misadventure” and “I wish my mom was a biker chick.”
Cylon and Garfunkel
Featuring Herman Menderchuck?
In the same vein, I’ll nominate Sgt. Pepper’s Lonely Hearts Club Band.
No shit! Thanks for fighting my ignorance. What the hell, Standells, “Boston, you’re my home” is a lie? Everything is all of a sudden upside down.
Aww, I thought I’d get to the end before my two got mentioned, but I’m gonna mention them anyway:
The Beets from Doug (I have this one!)
Love Händel from Phineas and Ferb (I need to get one)
Also:
The LumberZacks and Just Getting Started (both from Milo Murphy’s Law)
I dunno - the song they did together at the end was rather tepid. Sherman needs to do a solo album - “I Ain’t Got Rhythm” is one of the best songs in the entire series.
Lucky for you there are lots of different Electric Mayhem T-shirts—some official, but most probably bootleg. Just do a Google Images search and you’re bound to find some for sale.
Do Leningrad Cowboys count? 
I love pretty much all the music from P&F, and also Milo Murphy, from the same folks.
I want (actual girlband) Little Mix to cover “[Busted](Busted | Phineas and Ferb Wiki | Fandom Version)” from P&F. So good.
Can they do “Ready for the Bettys” too? 
Ooh, ooh. New number 1: Vitaly Chernobyl and the Meltdowns. Can’t get enough of that old-time Ukrainian nuclear fuzz-grunge.
Turns out there’s a website devoted to listing fake bands like this. They currently have 4,979 bands listed. 21 more to 5k!
Yes, Toad the Wet Sprocket is listed.