The GIMP is a raster image editor so working with TrueType and bitmap fonts is not the same as working with vector versions of the same in tools like Inkscape. However, GIMP has long been able to convert text into vector paths to manipulate to your hearts content.
Finding fonts is not that hard, but finding quality fonts takes time. Most free or publicly available fonts lack certain features that the high quality, expensive fonts provide, including some characters. Still, most online work and work for personal pleasure can suffice with the available free font collections.
The following list is in no particular order and no sites listed are recommended over any others. The list is simply a collection of sites I’ve run across related to freely available font collections.