No, it doesn't come in a 120” length.
No, it does not come with support brackets.
Yes, this product includes end caps.
Thank you for your recent inquiry with The Home Depot. We see the item (104 in. White Handrail Lineal) as a in store only item . It would be out of stock in your local store. We are not seeing a date for the back in stock of the item. We would suggest that you stop in your local Home depot and see a floor agent in the lumber department to see when the item would be back in stock .We are not able to check the inventory of a local store with the online service, We apologize for the set back. We appreciate your business and look forward to serving you in the future. Thank you for shopping Home Depot.
Hi Ray, please give us a call at: 1-877-279-4496
Hi moman, as long as your purchasing from the RDI Hand Rail line, all fo your parts should be compatible and color matched.