I found a couple[1][2] using GoodFirms. Looking at their websites, they should be able to build you an exchange for both web and phones.

I haven't used either of them though, so I suggest you do more research and not count on the reviews on the links below (as they can be fake).

[1] https://www.goodfirms.co/company/sodio-technologies-pvt-ltd
[2] https://www.goodfirms.co/company/bitdeal