I’m interested in getting a recommendation for a paper that I can paint directly on with oil paint and thinner and not have to prime it first.

Arches oil paper is recommended, but do you have a heavier weight paper that’s 300 lb? I believe they have one that’s 30 x 22, 140 lb, but I’d like it heavier.

What paper do you recommend and can you mail me some samples to try?

There is no perfect solution unless you gesso the sheet. Having said that, Arches Watercolor 300lb would be the best alternative though you might still have some bleed. Arches Watercolor has the best chance of standing up to the oil because it is double sized with animal gelatin. This means that in addition to the normal sizing put on a watercolor, the Arches mill adds a second application of surface sizing after the paper is made. This gives the surface better holdout for wet media and other similar mediums.