If by "quad rail" you're referring to the RIS/RAS handguards, you can get a CNC machined one in-country. I know they are available in the Retailer section. View the Airsoft Depot thread by Huang in the retailer section, you can clearly see the CNC Allwin RAS Handguard. I believe that this does not require you to be age verified to view or purchase. As always inquire about it.
I am not sure if the ICS SiG552 has a different setup from the typical TM Clone SiG552 (I've heard the ICS SiG552 is a bit different in some cases) in regards to the handguards, if not, it's a nice investment. The quality is quite nice considering the price is something like a third of what the Proud SiG552 Handguard. Speaking from experience, I have one installed. You can try asking Huang himself if he knows whether or not the handguard will fit on an ICS model SiG552, or perhaps someone has experience with it.
Primary: Custom WE M16A3
Secondary: KWA MP9
Side: Custom WE M1911A1