My engine has Clevite CB663H bearings and I cannot find them for sale. The listed replacement is the CB663HN and from what I can find out it is .030 narrower and 2g lighter.
Question... Are the CB663H bearings available? and If I have to use the CB663HN, will I have to rebalance?

the narrowed bearing should work fine in my opinion and is a better choice due to extra clearance on the radius . it shouldn't affect balance enough to worry about imo.

I would say zero effect on balance. all will be same weight and its on journal not out at other end. Thats .030 less contact on what? Minor percentage of bearing area. Look at it like this. lots of folks run narrower bearing to pick up power,so that's just bonus. How much Very little but hey its power.

I've run the "N" for a long time, though in a SBF. It can run either the regular CB663H or the CB663HN. I've run both and have noticed no difference in pressure, power or anything else.

Just looked up that bearing at my local engine parts warehouse(EPWI) the CB663H has been discontinued and replaced with the CB663HN

The N bearings came along when aftermarket cranks became much more affordable and available. Bigger radius on the cranks required chamfered bearings. Narrowed bearings eliminated the need to chamfer your own bearings. There is no problem using an HN in place of an H...

As said, no issues and your good to go.