The very popular spell checker spell from Keyoti has supported TX Text Control .NET for Windows Forms as of version 3.6.
Keyoti just releases a release candidate of version 3.7, which includes TX Text Control .NET for Windows Forms 13.0 support. This pre-release version can be already downloaded here:
RSDT.NET-3.7.0-BETA-Keyoti.spell.TXSupportv13.zip
Please have a look at this forum thread to get more details about this release.