My game is a simple text-based “life simulator”, but I want to make custom images for it to accurately represent the image I have of it in my head rather than using stock photos.

Where should I look/what are some tips to get started on this?

Offhand, a few options occur to me:

1. I presume that, since you mention using stock photos, that you don't currently feel up to creating the artwork yourself. One option, then, might be to practice your artwork until you are confident in doing so.
2. You could look around for assets and asset-packs (whether free or paid for) that might provide art closer to your vision than you've found in stock photos. There are a number of websites to which you might turn, I believe--itch.io, for example.
3. You might seek out an artist (or artists) to commission custom artwork from.

@Thaumaturge

Thank you for the reply! I'll look around and see if I can find some artists with the style I'm looking for; not sure how that slipped my mind.

Also keep in mind that there are tons of "amiture"= non pro artists out there that may be interested to work for less than you think.

Don't automatically jump to the conclusion that you need to pay for it.

[“amiture” = amateur] Look in the Hobby Project Classifieds. Click Forums at the left, then click Browse.

oops