Hi guys,
We are having problems with the specific state in Germany: Bayern. Therefore we want to block all users coming from this region.

I found that it is quite easy to block a certain country using the IP ranges, but how do you block a region from entering a website?
Is there any way to get the IP's of Bayern and then disallow these?

Only if there is one particular ISP (and ONLY one) providing Internet access to that area.

Hmm... Do you have any suggestions to how I can figure out if there is only one ISP?
And what could be done in case I found this one ISP?

Have a look here see if you can find one.

Try Geolocation databases and cross-reference their IP against it. There's at least 1 free db available; possibly 2 (if I can find the links again I'll edit this post). You may find that futile though because those users can just go through proxies to get around it.

There are some online sites that will give you a list of ips for an entire country whether they are totally accurate is another story. And for a city or region would be harder to find. The thing is even if you block an ip or range of ip's they can just use a proxy or one of those anonymous surfing sites to by pass if they really want. You would probably stop most of it, but there is always the persistent or determined one out there.

Sounds like you are getting ddos'd, Might want to see if you host has some sort of protection.