Confused about what cassette to buy

I'm very new to bike maintenance and I've been having a lot of fun with it! I have a Shimano Sora 9×2 groupset on a 2013 specialized allez compact sport. The closest model I can find is the 2014 specialized allez sport : https://www.specialized.com/us/en/allez-sport/p/49774?color=149429-49774

I'm not sure why the 2013 model isn't on their website.

The current cassette is Shimano HG-50, 9-speed, 12-27.

I have some wheels with 11s shimano hubs and I want to put a 9 speed cassette on it. I know I'll need spacers to do this, but I'm having trouble finding which cassette would be compatible. I've tried googling the specific cassette on the bike but I get conflicting information, as the parts that pop up have varying numbers of teeth.

Any ideas on cassettes I need to buy? Thanks!