There are quite a few out there, but it's not just as simple as the UFC "not choosing to sign them". There are a lot of other issues you have completely ignored. Fighters have contracts, the UFC can't just sign any fighter at any time.
Minakov - Under contract with Bellator
Kongo - 40, already been cut from the UFC.
Puetz - Solid prospect, usually fights at LHW, came up to HW to fight Tybura, highly doubt he'd fight at HW if the UFC signed him.
Kharitonov - Not going to happen, he wants to be able to compete in kickboxing etc, doesn't want an exclusive contract, would have happened by now if it was going to.
Tony Johnson - Under contract with Bellator. Boring style but would be a solid signing when his contract expires.
Grabowski - Would be a good signing, not exactly "young" but solid fighter.
Tybura - Won't sign him coming off a loss to Puetz but a win over Delija could get him signed once his contract with M-1 is up.
Golstov - Could and should be signed.
Ivanov - Signed to WSOF. Pretty inactive in recent times but hopefully that is now over. A few wins could see him UFC bound.
Volkov - Coming off 2 losses, under contract with Bellator.
Evgeny Erokhin - Coming off some good wins, should be signed.
Bedorf - Hard to see him leaving KSW. He, like Khalidov is earning a pretty penny and a company man and huge star.
Chris Barnett - A valid suggestion when he decides he wants to cut to 265 and not fight at 300lbs+
Derrick Mehmen - Contracted to WSOF, could sign after a few wins, fighting Ivanov next.
Smealinho Rama - Coming off a loss, solid prospect though.
Cody East - Solid suggestion, will probably get signed too, fighting for Legacy helps.
Alex Huddleston - Contracted to Bellator, good prospect, probably not UFC ready though.
John Hawk - Regional level journeyman, could add some depth to the division but not exactly "young" or that talented
Denis Smoldarev - Just bounced back from his first loss, signed to M-1
Ruben Wolf - 10-6, beaten a bunch of nobodies and lost to any noteworthy names (Puetz, Delija and Turek)
Satoshi Ishii - Mid level at best but would cost a lot of money to sign him, really not worth it.
Bobby Lashley - No. Signed to Bellator (Viacom) and TNA under the same deal, also 40.