You could create a table in Airtable with just one record where you store the last order ID you generated. In your program, you would then withdraw that number and increment by one to use it in that run, updating Airtable as well.
It is a clunky solution but it will work. In the future you should not need to use an external provider to share the value of a variable across different program runs but that functionality is not yet implemented.
Another option is to generate a random number that is really big (with 10 digits, for example): technically there could be two ids that are the same but the likelihood of that happening is really small.