One option is to call around to Volvo Penta dealers to see if they have any boneyard engines that they'll sell you a used pump off of.
The MD2B used a Bosch PFR 2K 75A/381/11 injection pump. Call around to diesel injector service shops and see if they can source the Bosch parts. If they can get Bosch parts, the price will be a lot better than the same parts in an official Volvo Penta box. (If they can't get the parts, Volvo Penta likely can't get them either.)
It might not be a bad idea to have an injector shop rebuild and calibrate your pump in any event.