UmAlQura Calendar in SharePoint

I was working on a calendar webpart that is used to display events stored in a MOSS list, each item in the list will have a start date and end date, when this webpart is added in an English site it shows Gregorian calendar and on an Arabic site is shows the Hijri calendar based on the regional settings for each site, but the problem was that the Hijri calendar is not accurate and the admin must go the regional settings page to add or subtract day or two to show the right dates.

On the other side there is the UmAlQura calendar which is based on an array that relate the start of each Hijri month to a Gregorian calendar day, It can be used for dates in range between 1318/01/01 and 1450/12/29 which is good to be used for articles dates and events and birthdates and so on.

So I changed the calendar format for my culture to be UmAlQura and it works perfect, but the problem is that the events are added in the list that is using Hijri calendar as a default for the Arabic site, and there is no UmAlQura calendar option in the regional settings to select, so I searched for how to make and add a custom calendar to SharePoint and found this link but still can’t find the answer

The other thing I found and it was very weird when I write e.Day.Date in the calendar cell (in the Arabic site) it gives me a full Hijri date (27/09/1430) but when adding e.Day.Date.Day it gives me the equivalent day number from the Gregorian calendar