So I have this problem for quite a while now, probably at most 2 and a half months. Note that I also have the exact same problem with Rust. Every time I start Gmod and look at the server list, it appears that there are no servers. I have looked at the Steam forums and it looks like other people have been experiencing this problem as well.
Can you connect through IP? Server list with IPs are here:
Use the console by typing
(e.g. connect 126.96.36.199:27015)