Here are a few you can check[1]. I'm not sure about the nature of your project, but none of them is going to give you any large sums. There used to be a list which I can't find anymore, but I don't think it had many more sites than this anyway.

[1] https://bitcointalk.org/index.php?topic=5487239.msg63759683#msg63759683

Personally, in the current climate, i wouldn't run a crypto mixing service even if that would mean my family would have to seriously cut down on basic expenses... It's just not worth going to jail over running such a service.

On top of this, you need to be a very good coder, since the slightest slip-up in your code could mean that either your mixer gets drained by hackers, or the anonymity of your users is compromised, or your workflow gets messed up, or LE gets on your tail.

Sure, if you don't look at the legal aspect and the risk of bugs/vulnerability's, the costs of running such a service are low, and if everything works flawless the risk of not running a profit is very low since you could basically dynamically adapt your fee based on the current optimal transaction fee + take a percentage... So you're basically guaranteed a (very small) profit on each transaction. You do need a ton of promotion to get some traffic to your site tough.

TL;DR;
Personally, i would strongly advice against running a mixer (and this is coming from a crypto veteran with enough relevant coding experience) because:

• you will get targeted by law enforcement sooner or later
• you will probably get targeted by the tax authorities
• you will need to be an OPSEC specialist
• you will need to be an excellent coder
• you will need to invest tons of time to gain a good rep

So, basically, you'll need to invest tons and tons of time (and a little bit of money) and you'll be in constant risk of going to jail, getting audited, getting your mixer drained, hurting your client's anonimity or finances... And in return you'll get profit... For me, it just wouldn't be worth it.