No, not really. There are multiple aftermarket cylinder head manufacturers, but they're hardly "John Doe" companies. They're small by GM/Ford/Chrysler standards, but it takes serious money to develop a head, let alone build the tooling and provide heat-treatment and machining facilities for volume production.
Companies don't advertise, but I think a lot of the aftermarket parts are designed/engineered, then subcontracted to companies that specialize in foundry work, not specializing in cylinder heads in particular. The raw casting maybe gets shipped to yet another company that does heat-treat, and then a third company that does machinework. The name printed on the box isn't the company that manufactured the part, but they paid the invoices for the other companies that actually did the work.
Not much different for forged cranks. Building the forging dies, finding someone with a big-enough forge to pound that much steel...and then taking the raw forging through the heat treat and machining process to make a usable part out of it would be hatefully expensive. Forged rods would be easier just based on the smaller size of the part to be made.
Way back last century--around 1992-ish--I looked into getting a reproduction aluminum intake manifold for Chevy 427 Tri-Powers cast for small-volume production. I was hoping that the folks who GM subcontracted to make the originals still had the molds and core-boxes and the other tooling. They could just pull that stuff out of storage, and pour me a hundred copies. Original, used manifolds were going for near $2K, and Holley was still selling the Tri-Power carburetors. I wound up with a packet of info from GM regarding the legal responsibilities of reproducing what had been GM part numbers/intellectual property; licensing fees, business plan and projected sales...the costs started at 20K before a single prototype manifold was poured, never mind getting the raw casting machined and put into a box. Needless to say, ten or fifteen years later someone else started selling those reproduction intake manifolds--I've heard they are poor copies, and made in China. And casting an aluminum intake manifold would be easy compared to casting and machining an aluminum cylinder head. Iron is even worse. The metal is cheaper, but the tooling costs more.
Getting a cylinder head manufactured and ready for sale is a major undertaking. An engine block would likely be worse.