I am looking for ideas mini sandwiches or sliders for a cocktail party. Am already planning on tenderloin sliders.

All open face and cut from small squares of Pepperidge Farm bread or a unique cracker: Egg salad, tuna salad, chicken, shrimp salad, salmon salad, sliced white meat turkey with a slice of classic baked dressing and a dollop of cranberry relish, a small zucchini pancake with a dollop of Crème fraîche, pulled pork is sauces with slaw on top.

What about smoked salmon and herbed cream cheese crostinis? Top with a bit of caviar and dill to add some flare. Or, how about a crostini with ricotta, duck proscuitto (can be found at a specialty shop, or maybe even Whole Foods), a berry jam and micro-greens?

not exactly a slider, but there are some recipes using avocado and curry that you could present on mini-pitas or lavash
https://food52.com/recipes/31594-julie-sahni-s-curried-avocado-with-garlic-and-green-chiles
https://food52.com/recipes/27617-curried-chickpea-sandwich

A nice summery idea is cocktail rye slice with herbed cheese, a cucumber slice topped with a small shrimp.

I love arranging prosciutto, jam (use your fav or make your own) cheese (brie or goat) fresh basil and crushed red pepper on little slices of baguette. Yum! Hope you find what you need.

A play on this sandwich would be good for vegetarians: https://food52.com/recipes/12703-grilled-garden-sandwich

Since you have a meat option, maybe do some eggplant Parmesan sliders on small ciabatta rolls or small squares of focaccia? If you leave off the cheese they would be vegan friendly as well, plus they are tasty at room temp.

I think these Korean meatballs would make great mini sliders, sort of a rift on a bahn mi. I would pile them on with an Asian slaw and kimchi and cilantro.
https://food52.com/recipes/21537-spicy-korean-style-gochujang-meatballs

I have served char sui pork with grilled pineapple on King's Hawaiian rolls. Not a lot of work and very tasty.