iOS 5.1.1 and below blobs are saved automatically through Cydia assuming the device was jailbroken at the time that the iOS is being signed. Meaning if you want iOS 5.1.1 blobs saved on Cydia, you had to have opened Cydia at least once when iOS 5.1.1 was the latest iOS on the market. If you did not save them manually using utilities such as TinyUmbrella or RedSn0w when they were being signed, you cannot save them anymore, there's no way to get them. If the device was jailbroken previously, you can open up Cydia, and scroll down to TSS Center on the Cydia main page on the device, open it up, and see which iOS are listed at the top.
Since your 3GS has a new bootrom, you cannot unlock the device free using UltraSn0w, you'll have to go through the carrier to get an unlock assuming they allow it
Since your 3GS has a new bootrom, you cannot unlock the device free using UltraSn0w, you'll have to go through the carrier to get an unlock assuming they allow it