As no one else has responded, I will do my best. Gold, particularly modern gold, is not my speciality.
First of all, welcome to the forum. I hope you stick around once this particular query is resolved.
I am not surprised the dealer company you spoke to offered only gold spot price. That is the default solution for most coin dealers and jewellery outlets as that way they are covered if the goods prove unsaleable at a premium.
If you want to sell them as one lot, a dealer is the most likely option, unless you can locate a collector with deep pockets who wants all of them. You will get better value by breaking the collection up and selling pieces individually. There are two main ways of doing this:
1. The easy way is to use an auction house specialising in coin sales, who will list it as multiple lots. You will, of course, lose out to the commission, both buyers and sellers, that they will charge, but at least the market will dictate the hammer price. If you go down this route, give us some idea of where in the country you are so we can suggest a convenient auction house.
2. The most profitable way is to effectively become a dealer yourself for a while, selling through online platforms such as Facebook or Ebay, or even taking a market stall somewhere. You will get a much higher price for the items, but have the hassle and expense of the process. You will also have to handle the occasional dodgy buyer, particularly when selling online. If you go this way, you will need to do your research to know what price to ask, using published online auctions and/or Ebay as a guide. (Remember with Ebay that it is the actual sale price that counts, not the often ridiculous asking price!)
I hope that helps.