Hi,
If you are organising conferences overseas then these should fall under the general rule whereby the place of supply is deemed to be where your business customer belongs.
You can see guidance here:
The place of supply rules for services
If you make supplies which are outside the scope of VAT then you are still able to recover this VAT as input tax as long as these supplies would be vatable in the UK if made in the UK.
Please see the guidance below, section 2.7:
Background to place of supply of services
Thank you.