You could consider the seat from OpenWheeler. It retails for $199 (USD) and has the appearance of a racing seat with the side bolsters but it does have a cutout for center-stick mounting and comes with sliders that support mounting to aluminum extrusion.

https://www.amazon.com/gp/product/B092LMYYYM

The listed images are of the older version without the center cutout but a few folks have reached out to their customer service recently and they confirmed they are shipping new orders with the cutout found in the listing for their full cockpit:

https://www.amazon.com/gp/product/B0BPMN53GW

Hope that helps!