The very popular spell checker RapidSpell from Keyoti has supported TX Text Control .NET as of version 3.6.
Keyoti just releases a release candidate of version 3.7, which includes TX Text Control .NET 13.0 support. This pre-release version can be already downloaded here:
RSDT.NET-3.7.0-BETA-Keyoti.RapidSpell.TXSupportv13.zip
Please have a look at this forum thread to get more details about this release.
There was a proplems with previous version.
"Incorrect selection in read-only Text Feilds while spellchecking"
Has this problem solved in this new version?