You can usually find those easily on eBay so you can buy another for parts. Thus, you can ask to make sure that when you buy another one for parts/repair, that it has a good hairspring. Examine the balance under magnification to make sure that the balance staff has both pivots intact and are not bent or badly scored. If it is damaged, you should be able to find a replacement online. If you do a look-up and find the part number, you can search ebay or some of the suppliers for the part. Additionally, the safty roller should have a jewel that isn’t cracked or missing. Then you go on to the pallet fork… and on and on it goes.
I hope this helps,