How do I find an accountant that specializes in online selling for small businesses? I don't know how to files sales tax and it appears to be very complicated. I sell on Amazon and ship my contents to their warehouses. My understanding is that I have to pay sales tax on items purchased from customers that live in my state (PA) and then also in the states where Amazon's warehouses are located. This is confusing and I need help as I am a new seller.

Due to Internal Revenue Service (IRS) regulations, U.S. third-party settlement organizations and payment processors, including Amazon, are required to file Form 1099-K for U.S. taxpayer sellers who meet the following thresholds in a calendar year:
More than $20,000 in unadjusted gross sales, and
More than 200 transactions.
IRS regulations require non-U.S. taxpayers to provide Form W-8BEN to Amazon in order to be exempt from U.S. tax reporting requirements.
As a result of these and other upcoming regulations, the following sellers are required by Amazon to provide taxpayer identification information to Amazon:
All Professional sellers
Individual sellers that exceed 50 transactions in a calendar year, regardless of sales volume.

For more information, please visit: Amazon.com : Sell Online - Selling on Amazon - FAQ

If you hire an accountant, you might as well not sell on Amazon, or sell on Amazon but do your own shipping. That way you only have to collect sales tax on shipments within PA. I can't see how you are making any profit shipping your items to Amazon.
Or sell on eBay.
You get a tax ID by contacting your state. It's very simple. You can do it on pa.gov. They send you everything you need to do, and if your sales within state are low, then you will only have to submit taxes once a quarter or half year, or even at the end of the year.