If you are interested in butterfly gardening, please consider picking up this book at your library-
Prairie Bindweed will definitely attract butterflies if it is planted where the species it evolved with exist and that would be over on the continents of Europe and Asia. Over here on the continent of North America where Prairie Bindweed has naturalized, it doesn't do much for any of our native butterflies as it isn't an actual host or nectar source of any consequence but bees sure do seem to be attracted to it.
Prairie Bindweed is a serious weed throughout North America.
It's a major threat to our crops as you can see above.
You might want to reconsider tracking seed down to this plant no matter how beautiful you think it is because we've already released one biological control to try to help out our farmers and several other prairie bindweed biological controls being trialed are on the horizon. You can read about the Eurasian noctuid moth (Tyta luctuosa) that was imported and released below or just skip to the wikipedia entry beneath which is short and sweet-
Here's the wikipedia entry on Tyta luctuosa which pretty much spells it out-
The larva is a brown caterpillar. The larva is the destructive stage. It eats leaves and flowers, especially new buds. This is the desired effect of this moth when it is used as an agent of biological pest control against field bindweed (Convolvulus arvensis). It was first introduced into the United States in the 1980s to attack this agricultural weed, which is its main foodplant.
If this Eurasian moth is successful, and I believe it has been so far in areas where it has already been released, its populations will grow and spread out in search of new food sources which will negatively impact prairie bindweed growing outside of the original release areas. This moth isn't exactly discriminating. It won't differentiate between prairie bindweed growing in your yard and prairie bindweed growing in a farmer's field when it's hungry. Biological controls imported to control invasive species are considerably more successful these days.