Some 31 IVs are preferred but not necessary. I'm willing to trade 1 of the following of your choice for Larvesta and 1 for Shroomish:
Male or Female Slowpoke with 31/x/31/31/31/31 IVs.
Shiny Male Slowpoke with 31/0/31/31/12/31 IVs.
Male or Female Heracross with 31/31/31/x/31/31 IVs and Rock Blast.
6IV Female Heracross BUT without Rock Blast.
Male or Female Sneasel with 31/31/31/x/31/31 IVs and Ice Shard, Icicle Crash, and Pursuit.
Male Skarmory with 31/10/31/x/31/31 IVs and Whirlwind and Brave Bird.
Female Pawniard with 31/31/31/x/31/31 IVs and Sucker Punch and Pursuit.
Female Buneary with 31/31/31/x/31/31 IVs and Fake Out.
Chansey with 31/0/31/x/31/31 IVs and Seismic Toss.
Chansey with 31/0/31/31/31/31 IVs BUT without Seismic Toss.
Male or Female Gible with 31/31/31/x/31/31 IVs and Outrage.
Male Gastly with 25/0/31/31/31/31 IVs.
Male or Female Drilbur with 31/31/31/x/31/31 IVs BUT without Rapid Spin.
Shiny Female Shellos with 31/31/31/31/31/3 IVs.
Shiny Male Shellos with 31/31/31/26/31/31 IVs.
Shiny Clauncher/Barboach/Heracross/Snover/Kecleon/Alolan Exeggutor/Slugma/Pinsir/Heatmor. (IVs are not quality.)
Any Starter. (You will have to wait for it to be bred first.)