Okay, try these sites ...
Arriscraft ... Arriscraft have (as far as I'm aware) seamless textures of ALL their products here ... https://www.arriscra...a32c09f534a.zip
Techno-Bloc ... I haven't looked as the textures so they may not be seamless, are here ... http://techo-bloc.s3.amazonaws.com/images/Techo-Bloc_JPEG.zip ... EDIT: Now I've looked at them ... Definitely worth a download.
Rinox ... Again, I haven't looked at them ... You may have to search in these files ... https://www.dropbox....h17p3mltXa?dl=0
Brampton Brick ... I believe that they have seamless textures but you may have to contact them directly. They are not obvious on the website.
Permacon ... This PDF says that there are seamless textures for download as it says "Don't forget to download the library from the Permacon Support web page for professionals." ... https://permacon-web... guide 2018.pdf ... but it's not really obvious where they are. You might want to contact Permacon and ask for a link to them. EDIT ... Try this page ... https://permacon.ca/...ssional-support. These install with a MSI (Microsoft Windows Installer) file. Navigate to the correct Softplan texture folder during the install. Again, lots of textures well worth a download.
Shouldice ... Shouldice DO have their textures as available seamless textures, but again not obvious on the website. We contacted Shouldice's technical department directly and they provided them for us.
Once you have all the textures available to you, make new folders as appropriate under C:\SoftPlan\3D\Textures\Bitmaps (your path may vary), and place the downloaded textures in those folders. They should be then available for use.