upper reciver

I am looking for an upper receiver and need it within a month - specific a Sig Spear LT 556 11.5 inch barrel upper ands his hand guard, with all the internal and external mechanisms on real scale on precise model.
After the conclusion, I will submit a redesign on some external parts.

Here is some resources, but this one is on 7.62, i will need on 5.56: https://www.cgtrader.com/3d-models/military/gun/sig-sauer-mcx-spear-lt-replica-low-poly