They are available on eBay at various prices. Here are the results of a search for Simplicity 4519 and here are the results for 4651. Note that there are more in the eBay Stores... and more (presently) are available on a second page.

I used the pivot method in the Youtube video I linked to modify the front pattern piece - I don't think it's going to fit on the fabric, going to have to cut a new piece. The edge of the new armhole ends up right in the selvedge, and with only 3/8" SA I think the little holes are going to show. Plus since the narrowest point is 25" from the selvedge and I refolded to 12.5", the edge of the hem is right AT the edge of the selvedge, which is 1/2" deep so I know some holes are going to show there, unless we make it shorter. Well, then again, the hem is 1.25" deep (double the 3/8") so maybe that will be folded up into the hem and the part that actually shows will be OK. I don't know, I've got other things to worry about now. DH decided to help me this weekend by getting the deer/rabbit netting up around the garden (permanently installed T posts with ENT conduit extensions to 7ft). But he trenched 3 sides and filled in with bark mulch, I think to try to keep weeds from creeping in (he just didn't do the side where my strawberries are creeping in, so I can move them). Now the plastic pegs that hold the bottom of the netting don't have anything solid to hold onto, we're going to have to lower the netting and lay it out farther from the posts onto solid ground. I'm afraid that trench is also going to fill with water and become a breeding ground for mosquitos (maybe they won't like the bark mulch?). We'll see tomorrow - supposed to get 1" of rain tonight. But I think he's going to have to extend the trench to the lowest point and let it all drain into the (already swampy) low point in the back yard. But I can't say anything until after my fears are proven correct, b/c any time I question something he's done and suggest a modification, he "undoes" what he did (sometimes making the matter worse) and then ignores my requests for other projects. He built a 3ft high stone circle around our wellhead a few years ago for Mothers Day, it was lovely, but when I expressed concern that our (then) young child and cousins could get hurt climbing on it b/c it wasn't mortared, he tore it apart, never rebuilt it, and has ignored my requests to build a 1ft tall stone wall under our porch, while proceeding to build a 50-ft long retaining wall in the back yard to the south of the vegetable garden.

That number seemed so familiar I thought I might actually have it. Turns out the pjs I'm working on right now are Simplicity 3935. It might still turn up. I'm trying to get an organizational system going and for some reason to do that it seems like I have to destroy any previously existing structure so things get a little scattered. I also might have had it until a few months ago. I had another pj pattern from the same time frame as the one I'm using that was child/adult as well that I gave to someone on freecycle who was looking for one to make pjs for multiple grandchildren and needed one that went down to 18 months in sizing. I don't recall what number that one was.

I sew for my gdtrs, too, and it is great fun. I've made that dress a couple times! May I suggest you begin with version b if you've never sewn before as the neckline will be easier for a first-timer, and it is just as cute. Pattern sizes for children are fairly forgiving, and a style like this one is very forgiving. It is a twirly dress the four yo will love. If you need to adjust anything, it will be length. To make gathering easy as pie, try this instead of pulling the bobbin basting thread: on the wrong side, lay a length of thin yarn or heavy thread (I use one strand of 4-ply candle wicking) just inside the seam line and zigzag over it, being careful not to catch the pull-thread in the zigzag. Then just pull the pull-thread from both ends until you meet your marks on the section you are applying it to and, viola! easy gathering! You can leave the pull-thread in the seam. It won't show. Happy sewing to you. I hope you get hooked...I've been sewing for 40 years, have made hundreds of garments, and still have a ball sewing dresses for my five little gdtrs and two gsons, as well as their parents.