I did not expect a subpoena to be issued in the first place, without any test to see if the person has a valid claim.
If you're unable to find a lawyer, contact the court directly to seek advice on responding: you should be able to file a response yourself.
That said, keep in mind, if the person chasing you is willing to hire a lawyer to file in California, they're probably not going to stop pursuing you. They'll file again and again for different reasons in different jurisdictions. Cloudflare have your identity and will give it up every time they are asked to by a court, it doesn't take much for an enterprising adversary to get access to it.
At a minimum, get off Cloudflare immediately.
I intend to get off Cloudflare if they are going to behave like this.
While it may not solve your immediate problem of wishing to remain anonymous, it may be worthwhile writing of this to Private Eye. (https://www.private-eye.co.uk/). If they shine a light on you, shining it back may be your best bet.
As someone who runs a political blog in the UK, you are almost certainly aware of the magazine's existence. However for others, the magazine features a consistent section of the shameful acts one finds across local councils across the UK. While the readership is niche and the content is almost exclusively in print, not online, it has an outsized impact in media and political circles.
I did think about blogging about it. Unfortunately I don't think it will help.