A customer tried to get this kit in Europe and couldn't find the .620" length timeserts (3/8 x 16 threads per inch). I had to send them to him and they're about $3 each plus shipping. Same problem with the bottoming tap but you can grind off the tip to shorten it yourself (thats all they do is grind it shorter - see vid). You should get both taps - the regular and the bottoming and use both one after the other.
It seems like you should be able to get someone to order them for you.
The 3/8" studs pulling out of the head is a common problem.