I could only think of 'Virginal' having semi-double blooms but it tends to get larger than 6 feet...whereas the other doubles such as Manteau d'Hermine are much smaller at around a metre. Not much help, I know. Best of luck getting a more useful answer.

Thank you for sharing! Upon looking at Manteau d’Hermine, it does have a similiar bloom shape.

in this type of situation... you look up propagation of said plant.. and then go beg some cuttings if possible...

it really is the only sure way to get the EXACT plant...

a potted shrub of this vigor.. is surely pruned heavily often... and the usual rule is just after flowering.. so your timing might be perfect.. if only you can propagate at this time of year ...

ken

It would be a really good time to consider doing semi-ripe cuttings, as soon as the bloom is over. Very easy plants to take cuttings from and guaranteed to get the same variety as the mother plant. Using a cloche or other closed cover keeps the moisture and humidirt just right as long as the cuttings are in bright shade - not direct sun.

A double flowering Mock Orange in mid Wisconsin (zone 4a) leads me to think it's likely one of the U of Minnesota cultivars.

@ken_adrian Adrian MI cold Z5 and @rosaprimula UK (Cambridge) Z8/9 thank you for the propagation tips and encouragement! I am really bad at propagation, but you are right--I should keep trying. Is there a cloche you recommend, or do you make one yourself out of an old soda bottle?

@maackia THANK YOU! This is a brilliant suggestion. I looked at all of University of Minnesota cultivars, and the shrub I found in WI looks a LOT like their "Snow White" cultivar. I will see if I can find a reasonable price online and order it (I've found a seller that was charges over $100 for this cultivar--nope).

I would echo rosaprimula’s statement about how easy they are from cuttings. We used to just shove short lengths into the ground in late summer. They’d be rooted by next year. You don’t need any special equipment to do them in a pot. A plastic bag over the top will do.

@floral_uk z.8/9 SW UK wow! I had no idea they could take so easily, even without rooting powder. Interesting to hear they would root by the next year. My soil has a lot of clay, and my understanding is that for propagation, a potting mix with vermiculite and seed starting soil is preferred for best results. I am always worried about how I would water the cutting and how to keep fungus at bay. Thank you for sharing! I will try again with my existing mockoranges and report back.

Take a lot and then a few losses won't matter. In pots it sounds as if you might be at risk of overwatering. The mix only needs to be slightly damp. Until the cutting has roots there is no way it can use much water. It just needs to not dry out.

Snow White Sensation maybe?