Alternatives to knobs for kitchen cabinets?

Builders being who they are, they probably didn't include knobs to (a) save the $1 per knob plus installation time or (b) that was the "look" at the time.

I would actually recommend U-shaped pull handles rather than knobs. Much easier to get a grip because you can "grip" like a knob (hand around the pull or knob) but also stick a finger or two inside the open space to pull. With any pulls or knobs, you can substitute longer screws.

Measure the thickness of the doors & drawers (drawer fronts are sometimes thicker than the doors) and then go to a hardware store. Home Depot and similar big stores have a fairly decent selection, in my opinion, or you can go to more of a specialty store, depending on your location.

I do recommend going to someplace you can (a) describe the doors and dimensions so they can make sure you get the right screws and (b) see and feel the items as some are much easier to grip than others, rather than trying to order online.

For oak (or other wood) cabinets I would probably go with a metal or metal-look plastic handle pull that matches other stuff in your kitchen - e.g., stainless steel or chrome if you have any stainless steel appliances, or brass or similar.