Hi Randy,
There are several American flagpole manufacturers who produce what they call hurricane rated flagpoles. These usually have much thicker walls around 6mm or even 8mm, however they mostly only go up to 10 inch diameter and many only go to 50 ft in height. An internet search can usually find these and then they can be contacted individually. The cost from the factory is usually fairly reasonable but transport, customs and import duties can easily double this cost. Also the USA has initiated stringent export requirements for American manufacturers that discourage exporters from dealing with non USA customers. I have had several USA companies refuse to sell me articles because of these export requirements.
A search of Alibaba.com will also show several flagpole manufacturers, they will usually provide a more competitive cost than those from the USA, however they are usually more difficult to deal with and to tie down to an actual cost for the product delivered to your home country. They will give you an estimate and then when you place an order the price goes up significantly!!
Other options are fiberglass, wood and steel poles. Fiberglass is now extensively used for utility poles and light poles as well as flagpoles, so there are multiple options there but they do tend to be more flexible than aluminium or steel and your rig would need to accommodate this. I did not find the fiberglass masts on Arcadian a problem even though they did bend quite a lot when she was sailed hard.
There are several manufacturers of stainless steel flagpoles that might provide a suitable pole.
Ordinary steel may also be an option as custom fabrication in your home country is more readily available so delivery and import costs are kept lower even though the original fabrication cost could be higher. Additional care is needed in finishing to prevent corrosion and ongoing inspection and care is required to forestall any corrosion problems.
A search of local small sawmills may uncover a local source for solid wood masts. These have been used for centuries and are a proven option, the main problem these days being finding a source for quality logs and getting someone to shape them. Your heavy displacement boat should have no problems with the higher weight of a solid wood or steel mast.
Plenty of options to consider but be very careful to get all of the contingent costs included as these can double the cost of the section delivered to your door and can often mean that something custom made closer to home may end up being the best option.
All the best with the search, David.