Hello!
I´m afraid that most wrecks in Kattegatt are a bit too deep for recreational diving and divecenters don´t run regular trips to them. There´s still some good diving though (naturedives) which may be different from what you´re used to.
In gothenburg I´d recommend
www.flyingdivers.se
There´s also
www.aquarius.se which is ½-hours drive south of gothenburg.
Flyingdivers start running trips in march.
If you want anymore info, just ask.