Proxychains with a standard nmap scan will work. My question to you would be why you would need TCP syn scans? Of course, they’re nice, but for ordinary recon, a standard nmap -A scan will do plenty.
Another thing I would recommend looking into is hooking into the Shodan database. They’ve scanned a lot of hosts slowly and with fragmentation, and they’ve already done the hard work.
Nmap actually has a NSE script to link in shodan, so potentially you could “scan” a public IP just by querying the shodan database, and that is the stealthiest you can get.
If you want something more aggressive. You may want to consider spinning up with a bulletproof host, or a VPS rented with cryptocurrency. This generally is what the bad guys will do. They’ll spin up a host with a fake identity, do their dirty work, and then burn it. I am not condoning doing anything shady, if they want to catch you they could get you through a correlation attack, so always use tor when connecting/provisioning a ‘burnable box’.
On top of this idea. I have had the idea to use Ansible to quickly provision pentesting boxes. @fraq 