You can buy the Poly-vi-Sol with or without iron.
They also sell a Tri-vi-Sol (or also Tri-Vi-Sol w/ Iron) that probably does taste a little bit better. It has Vits A,C, & D. Probably a better match for those first 6 mos breastfeeding.
Consider adding an iron source between 4 and 7mos through toddlerhood. Preemies are notorious for not making enough red-blood cells and are frequently anemic. If the vi-Sols aren't tolerated (the iron variety is usually the one that makes the flavor really awful!) you can use a bit of Floradix. It's a natural source of Iron (I think) that was digested easier and better tolerated flavor-wise by my dd. You can find it at Whole Foods, your local health food store, or as always, online.