Cannot register at forum.subsonic.org – all IPs banned

I'm trying to register at http://forum.subsonic.org/forum/ucp.php?mode=register but all IPs I've tried are banned.

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Your IP 201.221.131.203 has been blocked because it is blacklisted. For details please see http://www.stopforumspam.com/api?ip=201.221.131.203.
Your IP 201.221.131.203 has been blocked because it is blacklisted. For details please see http://www.barracudacentral.org/lookups/ip-reputation?ip_address=201.221.131.203.
An entry on the blacklist may have several reasons:

1. You are a well-known spammer.
2. Last time a well-known spammer was using the dynamic IP address which you got from your ISP (Internet Service Provider), your e-mail address or the username you have chosen.
3. Your ISP is well-known for a lot of spamming customers and is not fighting against spammers enough.

I've already tried my home ISP, mobile ISP, different Tor nodes, Opera Turbo, different free VPNs, different free proxies.

How can I register there?

(I've thought about asking somebody from another country to register there for me but I still hope to do that on my own.)