They're okay, but I would probably use: Sorry that I can't be of any help to you or just I'm sorry that I can't help you

Sorry, I can't be of any help to you, on this.

I would simply say, 'Sorry I can't be of more help' or 'Sorry that I can't help you.' But both of yours are fine.

They both sound natural enough. You can also say: "I'm sorry I can't be of more help to you in this regard." or simply "I'm sorry I can't help you."