Have you looked up at the handle, where the pin goes through the playfield bracket? Has some one put a bolt and nut through the point where the locking pin is suppose to be?

Even tempered glass is lower in price, than a used lock down bar.

If the lock down bar is unobtainable, then drilling through the bar, or cutting off the lock down bar is not an option.

Remove the legs, and backbox. First, get up inside remove the 10 screws holding the brackets for the play field, not as easy as it sounds. The plunger might be in the way, and may have to be removed too. Turn the pin on its side or upside down (on a hard surface or over a tarp), break the glass. Clean up all of the glass CAREFULLY. The playfield will be exposed, turn the game over, slide the playfield into the back of the game The playfield only needs to move back far enough to clear the lockdown bar. Then one should be able to pivot out the playfield. This should now give full access to the mounting hardware on the receiver.

Basically repeating what pinhead52 has already suggested.