If sold privately,, you need connections !! Major auction house for evaluation would be my suggestion !! And try to find one familiar with this collection !! They might act as agents for you for a fee of course !!
The auction house would charge commission. Very, very few would act as an agent between vendor and only one buyer.
A bit of research and some e-mails, contact the right people if confirmed, approach a few to see if they are interested.
A well known celebrity antiques expert in the UK spotted an item whilst filming a programme for the BBC. He had a buyer in mind so he paid the few hundred pounds. Not too long after he was paid five figures for it by a collector and didn't have to pay his 20% commission.
That's a best case scenario but it is possible to get more money privately.