Order a 50 lb sack and you're good to go. They still have it in stock.
I made a sourdough starter. It is kind of working, but some parts are tasting odd. There was also mold buildup at the margin
Throw that bit away and give it more flour and water (I use a 70g flour/100g water ratio). It'll be fine.
As for mould build-up, that isn't a good sign. It does happen and I know people who just scrape off the mould and move on with their lives but I'd personally start again from scratch.
The real problem is that I keep it in the fridge too long, when I do not need it
Btw, you don't need much yeast - just use less than 0.5 grams, let the dough rise for 8 hours at room temp. You can save that dough and continue making more bread from the culture.