Howdy,
PI Motorsports appears to have a candidate De Tomaso steering wheel center on ebay: https://www.ebay.com/b/Steerin.../33704/bn_7064364870
I did not notice a diameter specified for the part but I sent the seller a related message this evening; I'll post if/when I receive an answer.
I too would like to replace my current [Momo GT] wheel with a Momo Race model and I would prefer to have the De Tomaso center.
--Brian