There are some good websites and music blogs trying to document this eruption of 7 inch vinyl creativity. Most are seemingly compiled by people digitising their old records and scanning the sleeves (the latter are great social historical artifacts in their own right) and sometimes the vinyl itself in various glorious colours.
45 Revolutions is the blog linked to the bible for this kind of music - 45 Revolutions by Mario Panciera, an encyclopedia aiming to be the definitive guide to punk, mod, powerpop and new wave singles issued in the UK and Ireland from 1976 to 1979. The book itself is nearly 1200 pages long and covers 3000 singles.
Killed by Death Records covers a slightly broader time scale and demonstrates that the post-punk DIY single phenomenon was not limited to the UK, Ireland, America and Australia- the site includes lots of Swedish examples too.
Always Searching for Music has more of the same (but also some 1980s stuff) with a 1977 French example from Warm Gun.
Worthless Trash is good too, perhaps more power pop than punk-centred with stuff mainly from UK and Belgium.
Punk 77 is not a music blog with MP3 files, but does exactly what is say on the tin with lots of information about UK punk bands from 1976 to 1979.
You need to check these sites regularly, as music files are often only available for a limited period of time (though the pictures and text are still interesting on their own). Warning, this can be very addictive - I have spent the last week listening to 1977 classics from the likes of The Dils ('Class War' and 'I hate the rich'), The Nosebleeds ('Ain't been to no music school') and Some Chicken ('New Religion').