I had exactly the same problem, after moving to Maryland and required to display a front plate - the front plate's holes were slightly off on both sides, and no frame was supplied.
Some people simply take self-tapping screws and make new holes next to the existing ones, but I needed a secure place to mount the front plate (it has to last at least 2 years in MD!), plus I think hanging your tag off the bumper with just half the holes looks cheap (IMO).
I found a "universal mount" frame at Advance Auto/Pep/Zone for ~$5; I got the kind that had several horizontal and vertical slots, and used two 5/16" x 1" bolts to mount it (very securely, I might add) to the existing holes. Four 1/4" x 1/2" screws hold the plate to the frame (I did grind down the top 2 scews a bit so the tips did not come through the back of the frame into the painted part of the bumper).
So, for around $6, you can have a nice-looking front frame in the spot where Toyota should have supplied one!