Of course if any one had any real answer, everyone would be wildly successful. I'm not going to lie to you : I don't have the answer either.
But here's a few ideas to get you thinking :
Success is first and foremost a question of meeting a real and enduring need. Successful people have identified an immediate or future market need, as well as a great way to respond to it. Enduring success is a function of being able to continue to answer this need as it evolves, and as the competitive landscape changes.
I believe that true success requires a deep and profound understanding of the need in the market. Such understanding can only be acquired by asking questions. Some people therefore argue that successful people actually ask better questions (I think that's a Tony Robins quote) !
If you'd like to talk about this some more, feel free to schedule a call!
[5+ years experience in business development and sales strategy]
The best way to get your first client is, hands down, your own network. Assuming you're launching a consultancy in a domain of your expertise, exploit whatever contacts you already have from a previous endeavour / job.
As for finding your 2nd, 3rd... and 100th client, look into tools used by other consultancies. Depending on the field you're in and who you're selling to (unclear from your post) LinkedIn can be a great tool to identify potential clients and to find out where you can provide the most value.
When it comes down to how to approach clients and maximise the impact of your value proposition, you might find the books by Neil Rackham a valuable read (I would recommend "Major account sales strategy").
Feel free to schedule a call if you want to go more in-depth.
First and foremost, I believe that team and added value is everything for an early stage startup. Every founding member should be an indispensable asset to your business.
With regards to bringing in other experts as co-founders, ask yourself why this particular accelerator would make such a demand. Can you think of a reason why they would not reassured by your proposal to bring in these experts as hires rather than co-founders? Have you validated your initial approach with people other than angels (e.g. successful founders of hard-ware based startups)?
Lastly, ask yourself what your company has to gain by going forward with this particular accelerator. Do you feel they represent a unique opportunity that you could not find elsewhere? If so : see if there are ways to address their concerns in ways that that would be acceptable to you (e.g. appropriate vesting schemes that would protect your interests).
You say that conversion rates are 'dismal'; are you sure they cannot be optimised further? What level of conversion would you need to make your current business model work for you?
Optimising your conversion rate is all about the landing page. Minimise clutter, clarify your core message and immediately engage the user. A/B testing should help you optimise. Get as much outside feedback as you can and don't stop pushing until the metrics show you're right.