Trade evolutions have got to be one of the most unnecessary and annoying evolutions methods ever. All of the Pokémon that evolve by trade with a held item should just evolve by holding said item and leveling up instead of trading. For the rest that don't evolve with a held item this is what I'd do...

Alakazam
>Lv. Up Kadabra holding a Twisted Spoon
Machamp
>Lv. Up Machoke holding a Black Belt
Golem
>Lv. Up Graveler holding a Hard Stone
Alolan Golem
>Lv. Up Alolan Graveler holding a Magnet
Gengar
>Lv. Up Haunter holding a Spell Tag
Gigalith
>Lv. Up Boldore holding a Heat Rock in the harsh sunlight
Conkeldurr
>Lv. Up Gurdurr holding a Damp Rock in the rain
Trevenant
>Lv. Up knowing Forest's Curse
Gourgeist
>Lv. Up knowing Trick-or-Treat

Escavalier and Accelgor are a bit different though so this is what I came up with...

Escavalier
>Have Karrablast defeat a Shelmet
Accelgor
>Have Shelmet be defeated by a Karrablast

Last there's Slowking which I'd change completely from the rest of the hold item and evolutions. Here's what I got...

Slowking
>Lv. Up Slowpoke holding a King's Rock while you have a Shellder in your party

As a bonus I'll add Slowbro too...

Slowbro
>Lv. Up Slowpoke while you have a Shellder in your party

The Shellder in both these evolutions would obviously no longer be your party once Slowpoke evolves.

What do you guys think?