I bought a Goldlok doll house at an estate sale. I was wondering if there is somewhere I can get replacement parts & replacement furniture?

No, your sales contract is with Kohls. They supplied an item 'unfit for purpose', due to missing parts. Under the Sale of goods Act, it is their duty to exchange, refund or supply the parts need to be able to use it. Tell them what I have said above and that is the legal advice you have been given. Important parts in BOLD.

HomeVance is an unknown company that is just a trading name. They have no website. Probably made in China.

Here is Kohls Returns Policy. It states quite clearly you can return it. Take it back, buy from somewhere else and never shop with them again. Tell all your friends and do reviews on their Social Media sites.

Returns - Customer Service - Kohl's

https://cs.kohls.com > app > answers > detail > a_id > re...
Returns. The Kohl's Return Policy allows you to return most merchandise purchased in-store and Kohls.com for up to 180 days after the original ...

Amazing Deals on HomeVance Furniture ' Real Simple

https://www.realsimple.com > RealSimple Shop > Home
If you love to save money, then you'll love these new deals on HomeVance furniture. ... HomeVance Harper Metal Bed, Brown... Kohl's.

HomeVance Furniture ' Kohl's

https://www.kohls.com > catalog > homevance-furniture
HomeVance Furniture · HomeVance Catania Dining Table & Faux-Leather Dining Chair 5-piece Set · HomeVance Alaina Metal Bed · HomeVance Remmington Arm Chair & ...

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  HomeVance ' Kohl's

  https://www.kohls.com > catalog > homevance > CN=Bran...
  HomeVance Remmington Arm Chair & Ottoman 2-piece Set ... HomeVance 2-piece Salma Moroccan Trellis Side Dining . ... HomeVance Grayson Black Dining Table.
  
  ..

since you bought the machine at a state sale it would probably be a good idea to have the machine serviced.
you should be able to go from straight stitch to zig zag with out any problems.
if you move the dials or knob & the machine will not do a straight stitch then it needs to be checked

you need super grandad who can do anything like this from flatpack furniture to dolls houses and fix the car .