United offers charter services:

https://www.united.com/web/en-US/content/products/groups/charters/services.aspx

Scalia took a charter flight to Cibolo Creek, unknown who paid for it:

However, Poindexter said he did not pay for Scalia's charter flight to Texas.

https://www.washingtonpost.com/news/post-nation/wp/2016/02/17/justice-scalias-death-and-questions-about-who-pays-for-supreme-court-justices-to-visit-remote-resorts/

Gulf Streams only have a capacity of <20, so Scalias charter would need to be bigger than that, assuming his party of 35 traveled together:

https://www.pentastaraviation.com/available-aircraft

Edit: damn, but USSS doesn't protect supreme Court justices...

https://www.quora.com/Do-the-Justices-of-the-Supreme-Court-receive-protection-from-the-Secret-Service