If you're looking for gems that are yellow and purple, you may have a tough time finding them. While many gems occur naturally in those colors, they are usually quite rare. Depending on where you're looking, you may be able to find some of these stones, or you may need to look elsewhere.
One option is to try looking in local stores or online retailers that specialize in gemstones. Many of them will have a wide selection of gemstones, and your odds of finding a yellow and purple gem may be somewhat better. If you're unable to find what you're looking for there, you could also reach out to gem dealers, who may have access to larger and more specialized gemstone collections.
Finally, synthetic gemstones can also be an option. There are some artificial stones made in yellow and purple colors that are quite beautiful and would be worth looking into.
In any case, the key takeaway is to be creative if you can't find what you're looking for in your local area or through online retailers. You may want to look into other avenues, such as gemstone dealers and synthetic gems, to find something that meets your needs.