As other answers have said it is possible to weld manifolds but it's not easy nor guaranteed to be successful. A lot will depend upon where the hole is and how good the guy is doing the welding. Some just can't be salvaged.
Nine times out of ten you're going to be much better off just replacing the affected part - unfortunately as you've already discovered getting a replacement for yours might not be quite that simple. The manifolds for both the 1.6 Vti (B16A2 engine - manifold part# 18100P30000) and the 1.8 Vti (B18C4 engine - Part# 18100P9KG01) are now discontinued by Honda and as such are hard to get hold of and expensive when you can.
The silver lining is that aftermarket parts exist! Still not back-of-the-sofa change in terms of cost (£200-300) and since many of the ones out there aren't direct pattern parts but rather upgraded units you'll have to declare it to the insurance but it might be your best way of sorting it.
PS: You'll also need to be careful when ordering as I believe some won't fit if the car has A/C.