The usual suspects list is long, Spiro, Sperati, Fournier, Torres and even a relatively unknown very prolific forger Segui
90%+ of Spain forgeries are Postal Forgeries (Counterfeits) from a few dozen unknown forgers.
Thanks to the works of Francisco Graus, Enrique Bergua and others two rather unknowns have been identified but little is known of them - Bobes & Novella (apparently a restauranteur in Valencia)
Here are the samples I gathered, first from Bobes (who also made bogus color forgeries) & Novella (rather well made forgeries). Genuine on the left for comparison.
Bobes Forgeries 1851-1854
Including several Bogus color forgeries
1851
1852
Novella Forgeries
1851
1853
