Since it's Glu credits then keep playing svz1 until you get into wave 50 and remember to not spend anything on samurai vs zombies 1 and then spend it on the second game ( sorry for bad English)
Listen all you have to do is turn off your iPhone or whatever you have then get back to the game and it should show up because it's actually a glitch and it's not glu fault
You could still get them all you have to do is hack the game ( I don't know the link) just search on google Samurai vs Zombies hack tool and it will show you how or hack the game and it's 100% free or you could just buy them if you don't mind
When you get to high waves the zombies will become stronger and it will take like 3 to 5 hits to kill a strong ally so I think you should upgrade a ally that does a lot of damage like farmer spear horseman spear warrior handmaiden and froiste the bowman ( I think those allies may help you when you get into high waves)