"Under CCP 699.510, you can only get a writ issued once every 180 days."
That's not what CCP 699.510 says. It says, "a new writ may not be issued for a county until the expiration of 180 days after the issuance of a prior writ for that county UNLESS the prior writ is first returned."
The county sheriffs will return a writ to the court that issued it upon request.
Additionally, a judgment creditor can levy as many times as it wants under a single writ. A creditor does not need a new writ every time it wants a levy.