Thanks for considering Aspose.
After investigating this issue in details, we've come to the conclusion that we're unable to notice the "Font not found" issue. In fact the Brush Script MT font is correctly being used in resultant PDF document. First I've installed the Brush Script MT font over my machine and tested the scenario using following code snippet and the resultant PDF that I've generated, is in attachment. Please take a look.
Pdf pdf1 = new Pdf();
Aspose.Pdf.Section sec1 = pdf1.Sections.Add();
Text text2 = new Text(sec1);
text2.Margin.Top = 30;
Segment segment2 = text2.Segments.Add("This is TrueType font in Brush Script MT.");
segment2.TextInfo.FontSize = 20;
segment2.TextInfo.FontName = "Brush Script MT";
pdf1.Save("d:\\pdftest\\new_Brush Script MT.PDF");
PS, I've tested the issue using Aspose.Pdf for .NET v188.8.131.52