Hospitals will have scrubs to use for ORs and such. Talk to your other residents. Most of us still bought extra pairs anyways as they were better fitted and more comfortable. You can't use these for OR, but you could use them for night shift/extended shifts depending on your residency program.
Wait until you start. Some hospitals require only their scrubs, others let you wear your own. Most will have their own supply. Some won't. Some will only give you a certain number. Wait until you start to find out or ask other residents.