iirc, that to me looks like it's just for grounding. The other end probably connects to the body of your Celica somewhere.
Another bolt will be easy to find and should be simple to replace. Remove the old bits from the first bolt and replace it with a new 10mm. AutoZone or Pepboys can get you a bolt for under a buck. Have a tech walk out to your car to take a look, or bring the broken bolt head and body in to the store with you.
Provided that you are able to remove the body of the old bolt, finding a new one should be extremely easy.
as a side comment, your engine looks very clean from what I see in your photo