Against lapras you can try a golem with both rock attacks, but he will suffer against ice moves. Maybe primeape with low kick and cross chop, he won't take supper effective but you will have to dodge. Kabutops with stone edge and omastar with rock slide are good but rare, and their fast attack is not supper effective. The best and easier to catch option is jolteon, unless you leave in the only place of the world where there are no eevees. For Alakazam and Gengar the easier way I can think is a snorlax with around 1000 cp with lick, he will be supper effective against both and resist shadow ball and shadow claw. If you don't have that snorlax try a nidoqueen with bite and earthquake against gengar (probably the only use for the queen) and for alakazam there is not any very good option, maybe two 1200 FC/XS pinsir, if you dodge everything.
Prestiging against Lapras, Gengar and Alakazam
1) Which mons to use to prestige against Lapras? I have read that magneton does the job well but can anyone suggest something other than electric types. They are very rare in my area. Going to get my first electrode and raichu (due to increased santachu spawns) and have only 2 magnemites.
2) Also is it possible to train against Alakazam and Gengar due to their extremely high attack. And If yes then what should I use?
Answers
Haunter for Alakazam? Ghost types r effective against physic I believe? And are maybe wigglytuff with feint attack or nine tails for Gengar. For Lapras maybe golem or it's pre evolution the name evades me with 2 stone attacks ?? May be wrong though. I've never experienced prestiging against a Lapras I wish I had that opportunity.