What you are talking about is an orchard plum cultivar named 'Sugar'. It has been discussed on this site in the past, perhaps if you search GW an old thread is still available.

I can't find anymore information on the GW. I was at the farm stand last month and they small piles of plums the size of large cherries at the register. They were labeled "sugar plums" and they were delicious.

I am having a lot of trouble more information on these kinds of plums. (lots of 'dance with the sugar plum fairies, etc.) I wonder does anyone know anymore information on how to obtain a 'sugar' plum tree? I would really like to grow these myself.

The on-line book below,The California Fruits and How to Grow Them, mentions the Sugar Plum on page 276, which was developed by Luther Burbank in an attempt to supplant the California version of the Agen prune, which for some unknown reason could never rival the classic French prune.
All prunes have a high sugar content. People might even eat them and grow them if they were marketed as sugar plums, rather than prunes. There are a number of bigger and better "sugar plums" now, than BurbankÂs turn of the century cultivar. You might want to check with the farm stand, and see if you can find out if there is another name for the tree the sugar plums came from. It seems like people gave up on BurbankÂs original Sugar Plum over a hundred years ago. I couldnÂt find it listed from any nurseries either.
The traditional sugar plum referred to the poem is a confection made with a combination of available fruits, nuts and honey and/or raw sugar. AndyÂs Orchard sells them.

Here is a link that might be useful: California Fruits and How to Grow Them

I was under the impression that this referred to persimmons. Sugar plums are often mentioned in the context of Christmas, and the only things still on trees at that time are persimmons. I think I even verified this once, but I can't really remember. I'll have to look up an image of a sugar plum.

Wilson Nurseries wholesales Sugar Plum trees to retail nurseries. A search on their website showed a local source.
Andy's Orchard has some pictures of their sugar plum products. They say the original sugar plum confections were made with a combination of many available dried fruits and nuts, so persimmons could have been used in some recipes.

Here is a link that might be useful: Sugar Plum gift boxes

I had never heard of the fruit. But when I bought bare root fruit trees this year (when almost all inventory was gone), there was one lonely, overlooked beaten up bag that said "Sugar Plum Tree." I thought, "Well I've never heard of it but it sounds good". So its planted in a container and the leaves even look different from other plums. I began to wonder if it was an editable. So, I've searched all over with little info found except for the fairies. Finally I found a picture and it has the same leaves, so I guess I managed to get one of these great plum trees. And where did I get it from????? Unbelievably -- Home Depot!! So good luck everyone. Try this next season before bareroot season and get to the nursery manager to see if he can order some. I'm in So California and I got it at the Burbank or North Hollywood store.

I was searching for info on plums in my area and I just came across a reference to the methley plum being called a "sugar plum"
http://lockbriarfarms.com/fruit.htm

xena, I have never heard that name applied to Methley - I would say that orchard has things mixed up. Methley is by far the most common plum grown in these parts. It is relatively easy to grow and is good but not the best tasting.

Scott

my grandfather had one when i was quite young.they were quite delicious, but then i didn't have much candy so good fruit was very welcome. this one had yellow and orange colored fruit with yellow freckles. it looked big at 5 years of age, but was probably 10-12 feet tall, a single trunk, not like a bush or the american wild plum. anyone has a source please let me know. rick

I too found these plums at my local farm stand! Tiny but powerful, they are from the Metely plum tree.