It depends on where and how you want to do this, but you can query something like TIGERweb's blocks service.
This doesn't give you the long form, but it gives you everything else you need to make the long form.
Alternatively, you might look into the Census API: https://www.census.gov/data/developers.html
I've not used it to query out a single GEOID before, but it works wonders for returning census data from a simple query.
Can you elaborate on the context of where you're looking to do this? There are some other ways you might approach this.