According to ESTC, there is a copy of Volume 4 dated 1737 in the Huntington Library:

The tea-table miscellany, or, a collection of choice songs, Scots and English. Published by Allan Ramsay. Vol. IV. Edinburgh : printed for and sold by the publisher, and all the other booksellers in Britain, 1737.

I can't get a link to the catalogue record to work, but you can go to the ESTC search page and search on the ESTC no N46034.

So it looks as if vol 4 was published separately before being incorporated into the 10th edition. This edition of the volume doesn't seem to be available online.