How do I find large clients(300k-800K USD per annum) for these two use cases?

Here's a kind of stealth way to find your first sets of prospects...

Go to LinkedIn and do a search for job titles like Director of Operations, Operations Manager, etc. Make a note of the companies they work for.

As for the second, you may want to consult a good list broker. InfoUSA, Hoovers, etc. come to mind.

You may also want to look for professional organizations for operations managers and executives.

Look for related conferences, conventions, trade shows, etc. and see if you can get an exhibitor list. If the company is publicly traded, you can cross reference the revenue figures from public information filings with the SEC or annual reports.

Hope this gets you started...

Before any company is going to sink that kind of money into any type of service they will need some confidence. Or to put it the other way around your firm will need some credibility. There are no details in your OP so I don't want to make assumptions. If this is a big company with a solid track record then obviously you need to leverage the case studies of existing satisfied known-brand customers.

If this is not the case (which I suspect) you need IMHO a 3 phase sale.
1) get a face-to-face meeting or a skype meeting and pitch phase 2.
2) propose a paid pilot project which would cost anywhere from $10k to $50k. The prospect must come away from the pilot with some tangible value justifying the expense even if they do not choose to proceed to phase 3.
3) when the pilot is done sell them your main product.

This approach does not work for all types of tech, obviously so I don't know if it will work with yours. I do know from experience however that barring major brand equity (Oracle, SAS...) to get this size of sale involves a number of small but progressively larger sales where the vendor proves their ability to deliver.

You are at the wrong place

Most of the entrepreneurs on Warriorforum are into affiliate marketing, online publishing, digital product creation or marketing

OP should focus on certain areas of LinkedIn or existing platforms that cater to startups. I'm not sure if it's against the rules to list these so I'll just play it safe and not mention them. You can easily find such sites.

Get ready for the competition though. You're not exactly the first Indian BPO firm offering startup development / scaling support services

Look for such people in social networks in thematic groups.

Linkedin and list brokers that have up to date b2b info is where I would start.

The only way you're going to know about the problems that you're trying to address in your prospect companies is to do your homework. No one here knows enough about your business (like you do) to tell you the clients you should go after.

For #2 above, I would suggest doing more homework online using your best keyword phrases and topics (markets) of the segments of the business population that most closely match the solutions you can offer.

No one cares about your business like you do. No one is going to do your market research for you like you can.

The best to you,

Steve

Go hunting on LinkedIn Ads Pay Per Click tailor it to the exact demographic you are after.

This is common when targeting larger companies. Often, you have to get buy in from several players - tech people, operations people, C-suite executives like CFOs and CEOs.

The best way to start is to learn the company's typical buying process for tech investments. Who runs point (typically the Operations Manager or their designee)? Who else has to approve? How long is the typical sales cycle? Once you have a feel for this, you can mold your process to work with theirs.

This is where the "friend of a friend" concept comes in. You never know who someone knows. Start with your current network to fish for introductions/recommendations. Join LinkedIn groups related to tech operations. Look to trade journals and contact authors of articles who may be able to help. Follow the financial news for pieces about companies in your prospect pool underperforming or facing problems you could fix.

Me, too...