Went searching for the free downloads advertised in the manuals of guitar hero 3... and what do I get???? nothing that is compatible. spent at least a few bucks downloading songs to see if they work, but no. Here Sony is in the classic breach of advertising laws. as long as the game exists, the law states that any advertised free content should always remain available. Sony is clearly in breach of this. class action any one?
I did try to get help from their support, but all they said is to search the PSN store
So have you searched the store? I don't know what was advertised (which would be Activision's decision, not Sony's, if they were removed) but there are several free songs on the store.
We don't know what songs you're talking about, let alone what you mean by the songs being incompatible.
Here is a list of all Guitar Hero 3 Add-ons: https://store.sonyentertainmentnetwork.com/#!/en-u