Nice to have you on board
The next book will be the penultimate SH, Moon Breaker. Simon has just handed in the MS. So we don't have a street date as yet, but I'd think sometime first half of next year.
Being the UK makes getting Simon's books hard!! Because he doesn't have a UK publisher for hard copy (Jo Fletcher books do most of the titles in E book).
You'd need to order from somewhere like Forbidden Planet and get the US import.
We sometimes get a few books we can send out from here. If we get any of Moon Breaker I'll be posting the info here.