try adding your website in business directories. You might need to pay a monthly / yearly fee for this (depending on how big and good the directory is you might be looking at up to $1000 per year / few $100s a month, but if the directory is big and popular it will be worth it). I know this because the company that I've worked for (around 2015) participated in many nationwide directories here in Romania and we used to get traffic weekly from these sites. I don't remember whether this traffic had converted into sales, but it probably had, because this is usually quality traffic (those people willingly click through to visit your site)...
Something else you can try is search for 10-20 sites in your niche (better yet, in your industry) and try to partner up with them. Of course, this means cold calling / approaching them in some ways (maybe at business expos) that most people are not comfortable doing, but - again, from the time when I've worked for that company in 2015 - I know that managing to partner up with even a few of such companies can lead to passive, quality leads and sales over time...
Other ways that I can think of (but which I don't know whether they work anymore, so you'll have to do your own research on these) are...
- participate in relevant facebook groups (and on social media in general)
- google for "lead generation" opportunities / services (it will probably cost you a lot of money to hire these services, but if they're quality services you will get your investment back many times more, over time)
- try the good old PPC advertising (again, it will be expensive in the beginning, but if you have no other options...)
- google for forums related to your industry and advertise in them (forum traffic is one of the highest converting forms of traffic you can get, but you need to pay up, either money or your own time and involvement)
NOTE: in the above paragraphs, by "partnership" I mean you make deals with other companies in your industry, that are either similar to yours, or that perfectly complement yours, in exchange for leads, discounted supplies, whatever... Just look for 10-20 websites in your industry (not necessarily niche, but the broad industry that you operate in), and figure out (or outright ask them) what their struggles are that you can help with, and propose "you scratch my back, I scratch yours" type of partnership and then you both link back to each other's sites (yes, it's a link exchange, but - for some reason - google tends to never penalize this type of link wheel when it's done between offline businesses, I know this because the company that I've worked for in 2015 had crazy - 3-way, even 4-way - link exchange schemes without ever getting any penalties, so this works pretty well if you create a page dedicated to listing all of your partners, for example...)