There are now equivalents of $1000 bills in REAL MONEY. They are called one ounce GOLD COINS. Canadian Maple Leafs, American Gold Eagles, South African Krugerrands.
There are also fractional ounce coins.
And soonyy1967 has a good point: It is a pain in the a* to cash $100 bills; what do you think it would be like with $1000 bills?
BTW, many, many years ago, before non-government counterfeiters got real good, there WERE larger denomination bills.
FYI, government currency is a rip-off. See
What Has Government Done to Our Money? and The Case for a 100 Percent Gold Dollar