This IOSYS is pretty radical.
Blutonium Boy - Cocaine Bar, LSD Island ... it's not REALLY happy hardcore, but it's still off the heezy.
Also check out Anabolic Frolic. smile.dk have always sort of reminded me of happy hardcore too.
edit: omfg children of the night. I used to listen to this ALLLL the time. I totally forgot that I used to listen to happy hardcore. *off to find more.*
The lyrics are soooooooo bad.