I've been building some prototype boards for work with JLCPCB recently. There used to be an option to bundle parts from LCSC but that kind of went away. However, if you have a PCB order open you can get super cheap shipping if logged into the same account on LCSC.

I've been using JLCPCB's Global Sourcing service a lot recently. I can get DigiKey/Mouser parts sent to JLCPCB's inventory for assembly. The shipping is a bit slow but it beats having to manually assemble a few components not available at JLCPCB.