I don’t know about that specific one but I know a few brands have made them. AatP has this one but it’s sold out in everything but white. R-Series has this one though which I’ve actually had my eye on for a while. Those are the only ones I can think of that are currently available, but you may have some luck on the comm sales if you made a WTB post.

What style specifically? Because there are some brands that make back packs which are very Loli-able. BTSSB makes the Usakumya backpacks which are very popular, but are obviously best suited for Sweet. Some brands also make bags like this from time to time where the strap can be worn long or it can be modified into a backpack. Another option, which would actually be much easier to come by, was just to go with a bag like this with a strap that crosses your body. It isn’t really too far off from a messenger bag, but it’s still obviously Lolita and a lot of brands make them.

Loris carries replicas of them as well as other styles of heart-shaped purses. You can buy them from Loris with a shopping service or just through Qutieland or Clobba.

Something like this or this could be a good option. Both are very simple and Classic but they have elements like the scalloping and the bows that make them very good for Lolita. For maximum versatility I would suggest starting off with one in all black.

Instead of trying to find a bag with sweets or candies on it, why not just get a regular Lolita bag? Trying to find one that has sweets on it will really limit you, so you could go with something that’s obviously Lolita, but isn’t completely matchy-matchy. Something like this or this for example would work perfectly well with that dress or with a number of other dresses so it would be more versatile, and then if you wanted to make it more themed, you could add keychains to it. You can find cute keychains all over Etsy and Storenvy that would match the print of the dress perfectly.

I think the dress has a nice Summery feel so I think it would look really cute with a boater hat. Just something simple like this in cream. You could also go for a vintage look with a pillbox hat, maybe with a birdcage. Or if you wanted something more simple, you could just put some cream and pink flowers in your hair.
For a purse, I would say to go with something that doesn’t have a strap as a strap could get in the way of the bow on the front of the dress (or vise versa). Something very Classic with handles in cream would be nice, maybe something like this.

White tends to be fairly versatile with Sweet Lolita so it could be a good option. Another option would be to look at the color that appears most often in your wardrobe and choose that color, or whatever color you coordinate with that color most often. Like, say you wear mostly pink dresses, but you like to coordinate them with blue accessories as often as possible. If the case is something like that, go with a blue purse.

It’s from Axes Femme. I don’t believe it’s available on their site anymore, but I may have missed it. A few brands have made similar bags though, so you may be able to find that or another similar one second hand.

I think it’s really cute, the only thing I don’t like is the bag. As you said, it does clash with the dress. I would say use a non-printed bag in either pink or black, maybe a star shaped bag to match the clips because that would be really cute. Everything else looks fine though, I even like the striped socks because you aren’t overwhelming the whole coord with stripes or anything like that.