Actually the Illionois gaming regs specifically permit the sale of chips from the cage:

Section 3000.640 Exchange of Chips, Tokens, and Vouchers
a) Chips shall be issued to a person only at the request of such person and shall not
be given as change in any other transaction. Chips shall only be issued to
Riverboat patrons at cashier's cages or at the Live Gaming Devices and shall be
redeemed only at a cashier's cage.

I disagree with David Spraggs claim that one can't buy chips as a semantic game. For all practical purposes you can BUY CHIPS. The fact that the casino can require you to redeem them does not doesn't alter that fact.

In addition David's analysis is based upon language in the Nevada regs which obvioulsy are irrelevent to a discussion of what happens in Illinois. Illionois does not have the language that Nevada does that says chips remain the property of the licensee.

Illionois however has a regulation which says :

Each Riverboat may demand the redemption of its Chips, Tokens or Vouchers
from any person in possession of them and that person shall redeem the Chips,
Tokens or Vouchers upon presentation by the Riverboat Gaming Operation of
an equivalent amount of cash or check dated the same day on an account of the
Riverboat.