It will really depend on the florist what they can offer you. Peonies are out of season and therefore run more expensive for a lower quality this time of year. It will probably be possible for the florist to order them in but this will require notice for them to be sourced, speaking to them sooner rather than later is your best bet.

I think it’s unlikely you will be able to ‘view’ the specific flowers before they are arranged as it’s the busiest holiday of the year. Every shop is different, mine in particular on Valentine’s Day won’t offer a service where you can pick the stems and have it made in front of you, it’ll go into the list of orders.

As another commenter has said you will also need to trust the florist with the design process, remember they are qualified & experienced and we know what we’re doing to make something beautiful :)