Does apple still carries iPhone 4 back glass covers?

Apple wouldn't replace just the glass. The "repair" would be done as a full replacement in exchange for the damaged device. Apple currently lists $149 (plus tax) in the US for the iPhone 4. It will be different (possibly unavailable) in other countries. I'm kind of surprised it's still on the price list, but there it is.

iPhone Repair - Official Apple Support

iPhone model Other repairs (AppleCare+) Other repairs (out of warranty)

iPhone 4 See "out of warranty" fee $ 149

The iPhone 4 is considered obsolete. That means Apple no longer officially offers repair or replacement services for them.

You could check your local Apple Store and see if they can help you, but honestly, it's not worth fixing.

Just recycle it and get a new phone.

Your phone is 9 years old.

I seriously doubt anyone has parts for it.