You found the parts diagram and below that on the JD parts page is the part number...
22 - AM128998
Bumper
1 (INCLUDES (2) M84971, (2) 19M7867 AND (2) 24H1122)

Google AM128998 and hits galore @ around $44.

I took the hood off today and there was no way that I could successfully repair the breaks in the plastic. It sort of shattered, and would have been a jigsaw puzzel to put it back together again.

This morning I emailed the local John Deere Dealer with the ID information on my 14 year old John Deere and the description of the part I need. He checked his inventory and responded he had the part in stock and it would cost $44. Stopped by the dealer on the way home this afternoon and had the part installed in about 20 minutes.

I did the same thing for the guide wheels on the mower deck of the same tractor a couple of weeks ago. They did not break but after 14 years they were just worn out. Asked the dealer if they were in stock, he said yes and I picked them up.

Yet another reason to buy a John Deere, the easily available parts. If it was a Sears tractor they would have had to order both parts and the tractor would have been out of commision up for a week until the the parts were delivered, if they had the 14 year old tractor in the computers.

After suffering a similar break on my JD I got a brush guard off of ebay. It seems to do the trick.

By brush guard do you mean the standard auxiliary bumper? I looked at it but it seemed to need the plastic bumper for the hood to attach.

No I replaced the bumper but added a brush guard so I wouldn't break it again