How to find / verify gst number of client

Dear All

1) Is there any way to find the GST number of Individual / Companies online? If i know the company name can i find the GST number?

2) I need to invoice client on 1st July but i do not have the GST number available with me and client is not sharing the GST number what can i do? Can I raise the invoice without mentioning the Clients GST number?

3) What is any client has not obtained the GST registration and client is beyond the threshold limit can I raise the invoice for such client without GST number?

4) How to raise an invoice for International Client? Will the invoice format be same for an international client? 

Thanks

Prashant Dedhia