I would like to purchase a few addons and themes but I don't see an option to do so.

 

Even free addons say...

Quote

Sorry, you aren't permitted to download this file.

What am I missing?

Nevermind a Buy button just replaced the un permitted to download text.

 

Those in the future who encountered this should double check they are logged into their client account. If you just purchased or renewed on an existing account, signing out and in usually triggers the system to do a refresh.