How do you get your small USD bills?

[SeatBackForward]

Have an upcoming work trip to the USA and upon checking my stash of notes, all I have is a few $20 bills. I 've checked and most FX places need minimum conversions of hundreds of dollars - I use my AMEX/WISE for most expenditures so I literally only less than $50 in $1 bills? We all know these are still needed for light tipping at hotels etc.

Any ideas on how I can one go about getting a bunch of $1 bills before arriving in the USA?

 

[I love to travel]

Having learnt my lesson last time ( you always need small bills for tips) I now always come home with 10 $1 bills.
My only suggestion is on day of arrival go to a supermarket and buy lots of little individual ( 1 item) shops and get change that way.