Hi stanier,
While there is of course normally nothing wrong with proper applications of the "block outs" you describe, in the USA I believe some ductile iron manufacturers and/or fabricators can sometimes be quite responsive to e.g. expeditious production of special length spools, particularly when there is a critical need. Also, many different types of devices and means are available from various USA vendors that can essentially make the installation of ductile iron piping "field adaptable" (e.g. from the length perspective), such that even restrained joint piping inside or outside of walls can be quickly "cut to suit"/cut to length in the field). In the smaller diameter sizes e.g. in sizes up to 36" (~900mm) this can even be accomplished where needed with some piping styles and effective restraining devices that do not require field welding nor labor intensive and/or reliant bolting/rodding etc.
Field adaptability in even the very largest ductile iron pipe sizes can also be accomplished, and even with axial restraint capability if required in the layout, but the latter normally requires either field welding of rings or beads etc. with special welding materials, or special pipes fitted beyond cutting locations with special glands and or separate couplings etc. for rod harness restraining etc. Judicious use of such field adaptability can perhaps satisfy some impatience, by minimizing or eliminating need for unanticipated, special length "flanged spools".