Good list. Sounds like your friends are doing a lot of shopping.
Just be careful as lots of leather products here aren't high quality. There are all kinds of levels of quality here. Obviously better quality = higher price.
The highest quality leather is mostly exported outside of Argentina where people have bigger budgets. You have to be careful to check the stitching and seams to make sure it's well made. Feel it and if it feels very stiff or too rough it typically means it's treated and dyed to hide all the low quality imperfections with the leather. You can also smell it to see if it smells like chemical products. Genuine leather should smell like leather.
Lower quality and more affordable leather can be found on Murillo Street between Acevedo and Scalabrini Ortiz.
Sylvia y Mario has great stuff. They can do custom jackets. A lot of friends have used them and I have also gotten a jacket here -
https://www.silviaymario.com/
Nimes in Soho has great purses -
https://nimesba.com.ar/collections/todos-nuestros-productos
Other great purses -Las Cabrera (not to be confused with the steakhouse) -
https://www.lascabrera.com.ar/
Trendy purses and bags -
https://jackiesmith.com.ar/
La Casa de Las Botas makes the best boots! -
https://www.facebook.com/La.casa.de.las.botas/?locale=es_LA