These rifles are not in series production in China. They are being assembled in batches from existing parts. IIRC, the last shipment Marstar got in sold out in 3 days. If you want one from Marstar, and are prepared to wait, call them and get on the waiting list. If you want one now, pay the modest premium and get one from one of the retailers who still has some in inventory. The supply of these rifles is limited, and sooner or later its going to dry up. If you want one, make the arrangements now. Wait, and the cost will be higher.
I cannot see any point in asking on this forum when Marstar is going to get their next shipment. No one here knows. Ask Marstar. If they know, I'm sure they will share the information, and be pleased to take your order.