How long will getting calyrex and Spectrier take?

Been looking for a cool pokemon to do a endless run with, and that also would be cool to try in classic. And realized i never really see calyrex anywhere. shadow rider looks super cool imo. then realized that calyrex has a base 80 in every stat.... then also realized that if i reset enough i could get an early form change item. but the problem right now is that i dont have calyrex, or spectrier. but i looked at the wiki and both have the chance of being encountered through wave 40-50 (50 boss for calyrex, and 40-50 for spectrier) but how long would you think it would take?

Also, would like if there are any tips on how to speedrun through round 50 asap. Or on how to get ghost rider in an actual run asap. Thanks in advance for any tips!