A 10mhz board is the easiest route.
As a home owner the 16mhz boards do have a hum to them that you can hear when sitting in an idle state - drives some people nuts. I have my basement filled with Neon bar signs that have a more prevalent hum so this doesn't bother me anymore.
Since you have all the other aspects of the game (existing game chips) - a themed machine etc etc, you are entitled under the "right to repair" laws to a replace the chips.
Under this pre-text if you have a eprom burner you can easily create yourself a new set and some kind soul may be able to send you the binaries and you burn them yourself.
You will still need to buy blanks but mouser and others can supply those. An eprom burner is also good to backup your existing chips - I have broken/bent a number of chip legs over the years doing game changes and having backups has saved me a lot of aggravation of getting stuff shipped. I am based in Canada and we call it the $49 parallel as cross border shipping becomes stupid expensive. Buy something for a buck and it becomes $55 between shipping, import fees and customs brokerage,
On the NLG home page we have a number of banner adds for good vendors - note they have been given a banner ad at no charge because they participate and help out our members. I would suggest you call them and let them know your predicament and I am sure they will help you out in a preferred manner once they know your a NLG contributing member.