Weird question: An alchemist who wants to expand his formula list can do so by buying scrolls and copying them, as a wizard would. They can use wizard scrolls, and there is a lot of overlap, so this option works to acquire most formulae.
The problem comes in with the unique formulae, like Alchemical Allocation, which do not appear on the wizard's spell list (or anyone else's). Alchemists cannot use scrolls (except via Use Magic Device), so a scroll of Alchemical Allocation is not really castable. Still, can it be purchased for purposes of copying it?
At game level, there should be alchemists willing to sell common formulae (or apprentices willing to deal them under the table), at least to the extent that wizards are.