Where can I buy spices in bulk?

Store spices against mold

First, I'd suggest putting any spices that still look good (that don't look like there's mold or smell off, or anything like that), and any new spices you buy, in the fridge or even in the freezer, too bring in for a while - this should let them store securely for a while so that new spices don't grow mold.

Next, you should probably clean the drawer pretty thoroughly - moisture is an issue, but the presence of mold spores is also a requirement for your mold spices. If there's something moldy around, it's more likely that other spices will come in contact with the mold, as the spores get on hands or jars and get inside when you open and manipulate them. You can even swap out your spice drawer for the contents of another drawer and store something that the mold spores in that drawer won't do if you're not sure you're cleaning it.

For your new or newly cleaned spice drawer, you'll want to make sure it's as dry as possible, especially after you've cleaned it. Maybe line them up with paper or something else if you think the shape has gotten stuck in any corners or edges. And make sure any jars and / or condiments you return are freshly clean (or new). You can, as MirekE suggests, put a handful of desiccant packets in the drawer to prevent it from getting too moist in the future (you may want to watch out for the desiccant packets that sometimes pop up in other things to keep in the drawer if you don't always want to buy fresh). Or occasionally point a fan at the open drawer so that the airflow may dry out.

If you keep checking the drawer and keeping it clean and dry, you may be able to prevent the mold from re-infecting the drawer (and spices), or at least catch it early enough not to lose all of your spices.