My understanding is that GRM have taken delivery of a total of 18 chassis and can quickly fully finish the cars as needed.
It seems that the plan was pre-Covid, to fill up more cars with international drivers, both has-beens and younger drivers from the less powerful classes in Europe/UK, America, North and South plus Asia. The teams are equipping themselves to fettle extra cars with sponsored drivers.
If chassis are ordered in batches, then there will need to be a lot more interest to get the field past 18.