Yes, like you could be a Changeling and enter the Recaster PrC out of Races of Eberron, it is a 4/5 caster class worth the CL loss and one of the many things it does for you is rip any two Spells from any Class List onto your existing Class. I think there are a couple other PrCs out there that can do it, like Rainbow Servant, given that Venomfire is also Cleric Spell.
In addition, nearly any True Dragon can access Venomfire as an Arcane Spell allowing them to create a Runestaff with it. As a Magical Item you can make a successfully UMD Check to use the item as if Venomfire were on your Spell List. This ultimately means for a couple thousand gold you can access it, well really up to almost any five Spells when you think about it, either pretty easily which is what you're wanting. The catch is it does require a specific sort of crafter, which while broad, we are also talking about a very overpowered Spell. You may face respectable DM limitations in this area depending on campaign power levels.