They are not really that hard, they or similar air cleaners were on most EFI vans and pickup trucks. It is definitely more work, but they have no holes and use the 10" Commando/Charger air filter. They also have the opening for the Holley and later Carter/Edelbrock carbs. They are about the same hight as the original baseplate.
I just tried searching eBay and the net and came up with nothing....I'd do that in a heart beat if I could find one....doing the work to make it work wouldn't be a problem either.