May want to start with a search on LinkedIn for government contracting firms. Another place to look would be https://www.usajobs.gov which is mostly direct hire into an agency if you have the skill set they are looking for. Sadly I can't give much more information than that as I was brought into my firm by a random recruitment email on LinkedIn. You may be able to also find some leads on the GSA contractor directory, although a lot of these firms have kind of generic names so it may be a bit of a needle in a haystack.