SBA has resource partners like SCORE, Women’s Business Centers and Small Business Development Centers located across the country that provide free business counseling to individuals looking to start or expand a small business. Visit our local assistance guide to find your local SBA resource partners by entering your zip code. The blog on ways to forecast a new product and advice on forecasting for growth may also be helpful.  Good luck!

I've found that if you can locate someone else in the same category (in a
different market) and ask for their input about the sales ramp, that they
will often happily provide useful input.

E.g., a long time ago, when I started my CPA firm in one town I asked a CPA
friend in another town what sort of sales ramp I might expect. He said,
"well, shoot, let's look at what I experienced..." and then he started up his
QuickBooks-like accounting software and shared his actual numbers.

Those numbers differed from what I ended up later experiencing, but they gave
me a good idea about what was possible, typical, etc.

I later tried to do the same thing, pay it forward in other words, when I had
the opportunity to help another friend.

Obviously, you need to be talking with someone outside the area you'll
operate in.