You can get a replacement WGRS from H&R for less than $20, although they may have increased the price with their latest price increase. There are other aperture sights available, see Peep and Firesights in the FAQs.
See Long Range Sights for the BC and Target in the FAQs, Buffalo Arms has them, but you're not gonna like the price.
The 38-55 Target barrel has been discontinued as a rifle and in the accessory barrel program, the only way you can get one is a complete rifle somewhere, or a second hand barrel, post a want to buy ad in the NEF/H&R classifieds here. See the barrel fitting info in the FAQs for fitting it yourself.
Tim