You may disassemble your NUC first. Refer to this clip how to do this (your NUC is similar). See the P/N of the blower and on EBAY or Amazon for replacement.
As Leon says, some of the blowers are available through Amazon and eBay, but there are also a couple of online blower and fan dealers that you can order from. You need to open your NUC and remove the board so that you can get the blower manufacturer and P/N that you'll need for this search.