I know Keypoint hires 1099’s (non-credentialed) regularly, unless things have changed in the past year. Just about everyone on this board wouldn’t recommend them for obvious reasons.
Can’t speak to CACI, SCIS, or CSRA. To my knowledge people are generally FTE’s who switch to 1099. You may have luck with ISN or 1Force. Omniplex does DHS/ICE BI’s.
As for a retirement gig, I wouldn’t recommend it. The OPM payout rates haven’t changed in years and you don’t get reimbursed for mileage. Unless you’re in an area where the payout more than makes up for the mileage, I just can’t recommend it over FTE.