I see this part is not available anywhere online, Ebay or anyplace. It seems like it just doesn't exist anymore. Is there a chance that any of you guys happen to have this part intact on your bike so I can get a description, if not a picture of the piece all by itself? I would like to try to mimic something to make it work for my motorcycle. 

i.imgur.com/keFf6jq.png
I hope this done it>>>>

Again I was hoping one of you guys might have something like that. The seal that goes over top of the air box of a 1973 MX250 
I picture it being a very coarse very breathable foam and this piece called the patch is like a strap that keeps it in place but it's got screws in it somehow or something.
Thanks so much! 
 

not the part I see on partzilla. the part they list is on ebay though.

I've seen one on Ebay as well. At least it was advertised to be the very same part number but the seal was on the side of the box, not the top of the box. On mine I don't have that seal at the side, at least not on the illustration that I was trying to link. The seal that's on the Ebay version is directly underneath the side cover but my side cover (like it's illustrated in the Partzilla picture) has a foam gasket on the side cover that seals  the opening of the air box in the same fashion that the seal in the Ebay picture does. The eBay version seems like a different arrangement totally when it comes to sealing the box. It looks like it's for a later model or something. 
 It does look like they're selling the whole air box, just happens to have that odd part included with it also.
It seems I can't get the illustration in from Partzilla to show but it's in the 250MX Partzilla thing. Its a picture from that.I've seen one on Ebay as well. At least it was advertised to be the very same part number but the seal was on the side of the box, not the top of the box. On mine I don't have that seal at the side, at least not on the illustration that I was trying to link. 
Different seal

The seal Im looking for  
 

This place has them - dcplastics
Copy this and go to eBay-

1973 1974 Yamaha MX 250 360 SC 500 Air Filter Lid Case Holder 363-14412-00-00



On EBAY. they have a bunch. 

Thanks Rick, but that's actually the top cover for the air filter itself. I have that that's intact. I got the original metal one the screw all that's good. This seals the top of the air box and it's part number 30 under the page "frame-side cover" on the Partzilla website. 30SEAL
363-21269-00-00