I think there are two ways to accomplish this. First of all, you could just Set(PARKINGEXTEN=701) before you Park() the call. If there happens to be a call in 701 already, it will use the next parking slot.
The next way is a bit nicer because it accommodates multi-tenanting Asterisk servers. First of all, define your parking lots in features.conf.
[parkinglot_sales]
parkext => 700
parkpos => 701-709
findslot => next
parkingtime => 60
context => park-sales
[parkinglot_support]
parkext => 710
parkpos => 711-719
findslot => next
parkingtime => 60
context => park-support
Finally, define the dialing behaviour.
exten => 700,1,Set(CHANNEL(parkinglot)=parkinglot_sales)
exten => 700,2,Park()
exten => 701,1,Set(CHANNEL(parkinglot)=parkinglot_sales)
exten => 701,2,ParkedCall(701)
exten => 702,1,Set(CHANNEL(parkinglot)=parkinglot_sales)
exten => 702,2,ParkedCall(702)
exten => 710,1,Set(CHANNEL(parkinglot)=parkinglot_support)
exten => 710,n,Park()
exten => 711,1,Set(CHANNEL(parkinglot)=parkinglot_support)
exten => 711,2,ParkedCall(711)
I hope this is correct. I haven’t tested this specific dialplan code. I have it working in my own PBX, but I have it split into Macro’s, etc.