Perhaps the parts you are looking for aren't added to the workshop yet.

You can find specific Parts using the Workshops Search function and the Item Number, the Item Number can be found on sites like Bricklink

For Example https://www.bricklink.com/v2/catalog/catalogitem.page?S=colmar-6&#T=I (Under the Section "Set Inventory" you find a full List of all Parts with their item numbers)

Those Item Numbers are used in the workshop too so you can search for them.

For Example:

The Mug of the Loki Minifigure "White Minifigure, Utensil Cup with Reddish Brown TVA Logo on Gold Rectangle Pattern" with the Item Number "3899pb009" is not in the Workshop.

The above used example, the standing plattform for the Minfigure Black Tile, Modified 3 x 4 with 4 Studs in Center with the Item Number 88646 is already in the Workshop and can be found there

just go to collectible figures and its the latest one