I am reluctant to share that information as my competitors would take advantage.
As soon as you open the route it's visible anyway. Since you're based in Singapore and got 4500 NM range planes, the obvious options are to Europe, and there's no shortage of decent tech stops for that, like UTNU, UATG, etc. Eastern US, for which UOOO is perfect for you, or western US, where your best option is probably UHPP.
I'm curious which suitable tech stops you found that weren't allowed.